Handle API key NotFound error when registering routes. (#4967)

This exception previously caused  ./run_server.sh -e biomedical to fail:

**Before**
```
(.env) [~/datcom-website]:$ ./run_server.sh -e biomedical
Starting localhost with FLASK_ENV='biomedical' on port='8080'
Not in Google network:  <urlopen error [Errno 8] nodename nor servname provided, or not known>
Traceback (most recent call last):
  File "/Users/calinc/datcom-website/web_app.py", line 22, in <module>
    app = create_app()
          ^^^^^^^^^^^^
  File "/Users/calinc/datcom-website/server/__init__.py", line 344, in create_app
    register_routes_experiments(app, cfg)
  File "/Users/calinc/datcom-website/server/__init__.py", line 184, in register_routes_experiments
    app.config['GEMINI_API_KEY'] = _get_api_key(['GEMINI_API_KEY'],
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/calinc/datcom-website/server/__init__.py", line 71, in _get_api_key
    secret_response = secret_client.access_secret_version(name=secret_name)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/cloud/secretmanager_v1/services/secret_manager_service/client.py", line 1767, in access_secret_version
    response = rpc(
               ^^^^
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/api_core/gapic_v1/method.py", line 131, in __call__
    return wrapped_func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/api_core/retry/retry_unary.py", line 293, in retry_wrapped_func
    return retry_target(
           ^^^^^^^^^^^^^
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/api_core/retry/retry_unary.py", line 153, in retry_target
    _retry_error_helper(
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/api_core/retry/retry_base.py", line 212, in _retry_error_helper
    raise final_exc from source_exc
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/api_core/retry/retry_unary.py", line 144, in retry_target
    result = target()
             ^^^^^^^^
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/api_core/timeout.py", line 120, in func_with_timeout
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/calinc/datcom-website/.env/lib/python3.12/site-packages/google/api_core/grpc_helpers.py", line 78, in error_remapped_callable
    raise exceptions.from_grpc_error(exc) from exc
google.api_core.exceptions.NotFound: 404 Secret [projects/886336214270/secrets/gemini-api-key] not found or has no versions. [detail: "[ORIGINAL ERROR] generic::not_found: Secret [projects/886336214270/secrets/gemini-api-key] not found or has no versions. [google.rpc.error_details_ext] { message: \"Secret [projects/886336214270/secrets/gemini-api-key] not found or has no versions.\" }"
```

**After**
```
(.env) [~/datcom-website]:$ ./run_server.sh -e biomedical
Starting localhost with FLASK_ENV='biomedical' on port='8080'
Not in Google network:  <urlopen error [Errno 8] nodename nor servname provided, or not known>
[17:35:51][WARNING ][__init__.py:185] DataGemma routes not registered due to missing API key 
[17:35:54][INFO    ][util.py:585] https://autopush.api.datacommons.org/version is up running 
[17:35:54][INFO    ][web_app.py:27] Run web server in local mode 
 * Serving Flask app 'server.__init__'
 * Debug mode: on
```

server/__init__.py

@@ -22,6 +22,7 @@
 from flask import request
 from flask_babel import Babel
 import flask_cors
+from google.api_core.exceptions import NotFound
 from google.cloud import secretmanager
 import google.cloud.logging
 
@@ -54,7 +55,7 @@ def _get_api_key(env_keys=[], gcp_project='', gcp_path=''):
       gcp_path: The path to getting the api key from GCP secrets
 
   Returns:
-      API key if it exists
+      API key if it exists, otherwise an empty string.
   
   TODO: use this method everywhere else in this file
   """
@@ -65,11 +66,14 @@ def _get_api_key(env_keys=[], gcp_project='', gcp_path=''):
 
   # Try to get the key from secrets
   if gcp_project and gcp_path:
-    secret_client = secretmanager.SecretManagerServiceClient()
-    secret_name = secret_client.secret_version_path(gcp_project, gcp_path,
-                                                    'latest')
-    secret_response = secret_client.access_secret_version(name=secret_name)
-    return secret_response.payload.data.decode('UTF-8').replace('\n', '')
+    try:
+      secret_client = secretmanager.SecretManagerServiceClient()
+      secret_name = secret_client.secret_version_path(gcp_project, gcp_path,
+                                                      'latest')
+      secret_response = secret_client.access_secret_version(name=secret_name)
+      return secret_response.payload.data.decode('UTF-8').replace('\n', '')
+    except NotFound:
+      return ''
 
   # If key is not found, return an empty string
   return ''
@@ -170,12 +174,6 @@ def register_routes_sustainability(app):
 
 
 def register_routes_datagemma(app, cfg):
-  # Install blueprint for DataGemma page
-  from server.routes.dev_datagemma import api as dev_datagemma_api
-  app.register_blueprint(dev_datagemma_api.bp)
-  from server.routes.dev_datagemma import html as dev_datagemma_html
-  app.register_blueprint(dev_datagemma_html.bp)
-
   # Set the gemini api key
   app.config['GEMINI_API_KEY'] = _get_api_key(['GEMINI_API_KEY'],
                                               cfg.SECRET_PROJECT,
@@ -184,6 +182,15 @@ def register_routes_datagemma(app, cfg):
   app.config['DC_NL_API_KEY'] = _get_api_key(['DC_NL_API_KEY'],
                                              cfg.SECRET_PROJECT,
                                              'dc-nl-api-key')
+  if not app.config['GEMINI_API_KEY'] or not app.config['DC_NL_API_KEY']:
+    app.logger.warning('DataGemma routes not registered due to missing API key')
+    return
+
+  # Install blueprint for DataGemma page
+  from server.routes.dev_datagemma import api as dev_datagemma_api
+  app.register_blueprint(dev_datagemma_api.bp)
+  from server.routes.dev_datagemma import html as dev_datagemma_html
+  app.register_blueprint(dev_datagemma_html.bp)
 
 
 def register_routes_common(app):