Add basic relay support to Pbench Agent (#3460)

* Add basic relay support to Pbench Agent

PBENCH-1142

This changes the Pbench Agent `results` mechanism to support a new mode,
refactoring the `CopyResults` class into a hierarchy with `CopyResultToServer`
and `CopyResultToRelay` and an overloaded `push` to do the work. The `--token`
option is now required only when `--relay` is not specified.

In addition to `--relay <relay>` to push a manifest and tarball to a Relay, I
added a `--server <server>` to override the default config file value, which
should allow us to deploy a containerized Pbench Agent without needing to map in
a customized config file just to set the Pbench Server URI.

The agent "man pages" have been updated with the new options, and some general
cleanup left over from #3442.

_NOTE_: with this change we have a full end-to-end relay mechanism, but it's
simplistic. You need to start a relay server manually from the file relay repo
at `distributed-system-analysis/file-relay`, and supply that URI to the
`pbench-results-move --relay <relay>` command. In the future we'd like to
package the relay and allow management and hosting through Pbench Agent
commands within a standard container.

agent/requirements.txt

@@ -7,6 +7,6 @@ jinja2
 python-daemon
 python-pidfile
 redis
-requests
+requests>=2.27.0  # JSONDecodeError, TODO CVE-2023-32681 (2.31)
 sh
 state-signals>=1.0.1

agent/util-scripts/gold/pbench-results-move/test-23.txt

@@ -15,11 +15,11 @@ Options:
   -m, --metadata TEXT            list of metadata keys to be sent on PUT.
                                  Option may need to be specified multiple
                                  times for multiple values. Format: key:value
-  --show-server TEXT             Display information about the pbench server
-                                 where the result(s) will be moved (Not
-                                 implemented)
+  --relay TEXT                   Specify a relay server as
+                                 http[s]://host[:port]
+  --server TEXT                  Specify the Pbench Server as
+                                 https://host[:port]
   --token TEXT                   pbench server authentication token
-                                 [required]
   --xz-single-threaded           Use single threaded compression with 'xz'
   --help                         Show this message and exit.
 --- Finished test-23 pbench-results-move (status=0)

agent/util-scripts/gold/pbench-results-push/test-24.txt

@@ -14,8 +14,11 @@ Options:
   -m, --metadata TEXT            list of metadata keys to be sent on PUT.
                                  Option may need to be specified multiple
                                  times for multiple values. Format: key:value
+  --relay TEXT                   Specify a relay server as
+                                 http[s]://host[:port]
+  --server TEXT                  Specify the Pbench Server as
+                                 https://host[:port]
   --token TEXT                   pbench server authentication token
-                                 [required]
   --help                         Show this message and exit.
 --- Finished test-24 pbench-results-push (status=0)
 +++ pbench tree state