Add remote_provider = "..." option, replacing scheme-look-ups (#20240)

This replaces the over-complicated address URI scheme-based look-up from
#19827 for deciding on which provider to use with just a normal option
`[GLOBAL].remote_provider`. This defaults to `reapi`, to preserve the
current (stable) behaviour.

That is, now, one can set:

```toml
[GLOBAL]
remote_provider = "experimental-file"
remote_store_address = "file:///..."
```

Or similar.

Another item in #19694 

The commits are somewhat usefully broken up for review.

docs/docs/using-pants/remote-caching-&-execution/remote-caching.mdx

@@ -54,7 +54,7 @@ The values of the `ACTIONS_CACHE_URL` and `ACTIONS_RUNTIME_TOKEN` environment va
   uses: actions/github-script@v6
   with:
     script: |
-      core.exportVariable('PANTS_REMOTE_STORE_ADDRESS', 'experimental:github-actions-cache+' + (process.env.ACTIONS_CACHE_URL || ''));
+      core.exportVariable('PANTS_REMOTE_STORE_ADDRESS', process.env.ACTIONS_CACHE_URL);
       core.exportVariable('PANTS_REMOTE_OAUTH_BEARER_TOKEN', process.env.ACTIONS_RUNTIME_TOKEN);
 ```
 
@@ -65,6 +65,7 @@ Once the GitHub values are configured, Pants will read the environment variables
 ```toml
 [GLOBAL]
 # GitHub Actions cache URL and token are set via environment variables
+remote_provider = "experimental-github-actions-cache"
 remote_cache_read = true
 remote_cache_write = true
 ```
@@ -85,7 +86,8 @@ To read and write the cache to `/path/to/cache`, you will need to configure `pan
 
 ```toml
 [GLOBAL]
-remote_store_address = "experimental:file:///path/to/cache"
+remote_store_provider = "experimental-file"
+remote_store_address = "file:///path/to/cache"
 remote_cache_read = true
 remote_cache_write = true
 ```

src/python/pants/engine/internals/scheduler.py

@@ -68,7 +68,6 @@
     LOCAL_STORE_LEASE_TIME_SECS,
     ExecutionOptions,
     LocalStoreOptions,
-    normalize_remote_address,
 )
 from pants.util.contextutil import temporary_file_path
 from pants.util.logging import LogLevel
@@ -179,6 +178,7 @@ def __init__(
             parsed_javascript_deps_result=NativeParsedJavascriptDependencies,
         )
         remoting_options = PyRemotingOptions(
+            provider=execution_options.remote_provider.value,
             execution_enable=execution_options.remote_execution,
             store_headers=execution_options.remote_store_headers,
             store_chunk_bytes=execution_options.remote_store_chunk_bytes,
@@ -193,8 +193,8 @@ def __init__(
             execution_headers=execution_options.remote_execution_headers,
             execution_overall_deadline_secs=execution_options.remote_execution_overall_deadline_secs,
             execution_rpc_concurrency=execution_options.remote_execution_rpc_concurrency,
-            store_address=normalize_remote_address(execution_options.remote_store_address),
-            execution_address=normalize_remote_address(execution_options.remote_execution_address),
+            store_address=execution_options.remote_store_address,
+            execution_address=execution_options.remote_execution_address,
             execution_process_cache_namespace=execution_options.process_execution_cache_namespace,
             instance_name=execution_options.remote_instance_name,
             root_ca_certs_path=execution_options.remote_ca_certs_path,