chore(rcm): get connection on every request (#6753)

We get the connection on every request to ensure that the agent is
actually still available. If not, we might be attempting to read from an
invalid connection, causing the I/O operation to block.

## Checklist

- [x] Change(s) are motivated and described in the PR description.
- [x] Testing strategy is described if automated tests are not included
in the PR.
- [x] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed. If no release note is required, add label
`changelog/no-changelog`.
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer has explicitly acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment.
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)
- [x] If this PR touches code that signs or publishes builds or
packages, or handles credentials of any kind, I've requested a review
from `@DataDog/security-design-and-guidance`.
- [x] This PR doesn't touch any of that.

ddtrace/internal/remoteconfig/client.py

@@ -162,8 +162,7 @@ def __init__(self):
         tracer_version = _pep440_to_semver()
 
         self.id = str(uuid.uuid4())
-        self.agent_url = agent_url = agent.get_trace_url()
-        self._conn = agent.get_connection(agent_url, timeout=agent.get_trace_agent_timeout())
+        self.agent_url = agent.get_trace_url()
 
         self._headers = {"content-type": "application/json"}
         additional_header_str = os.environ.get("_DD_REMOTE_CONFIGURATION_ADDITIONAL_HEADERS")
@@ -257,14 +256,15 @@ def _send_request(self, payload):
             log.debug(
                 "[%s][P: %s] Requesting RC data from products: %s", os.getpid(), os.getppid(), str(self._products)
             )  # noqa: G200
-            self._conn.request("POST", REMOTE_CONFIG_AGENT_ENDPOINT, payload, self._headers)
-            resp = self._conn.getresponse()
+            conn = agent.get_connection(self.agent_url, timeout=agent.get_trace_agent_timeout())
+            conn.request("POST", REMOTE_CONFIG_AGENT_ENDPOINT, payload, self._headers)
+            resp = conn.getresponse()
             data = resp.read()
         except OSError as e:
             log.debug("Unexpected connection error in remote config client request: %s", str(e))  # noqa: G200
             return None
         finally:
-            self._conn.close()
+            conn.close()
 
         if resp.status == 404:
             # Remote configuration is not enabled or unsupported by the agent