chore(telemetry): fix ssi instrumentation tracking + fix failing docker_ssi test (#13609)

Fixes the collection of instrumentation telemetry for ssi. 

Note this is not a customer facing fix, a release note is not required.

Resolves the following CI error:
https://gitlab.ddbuild.io/DataDog/apm-reliability/dd-trace-py/-/jobs/968352550

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- 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)

Author: mabdinur

ddtrace/bootstrap/sitecustomize.py

@@ -166,8 +166,9 @@ def _(threading):
         else:
             log.debug("additional sitecustomize found in: %s", sys.path)
 
-    if os.getenv("_DD_SSI_INJECT_SUCCESSFUL"):
-        # _DD_SSI_INJECT_SUCCESSFUL is set in lib-injection/sources/sitecustomize.py after ssi is completed
+    if os.getenv("_DD_PY_SSI_INJECT") == "1":
+        # _DD_PY_SSI_INJECT is set to `1` in lib-injection/sources/sitecustomize.py when ssi is started
+        # and doesn't abort.
         source = "ssi"
     elif os.path.join(os.path.dirname(ddtrace.__file__), "bootstrap") in sys.path:
         # Checks the python path to see if the bootstrap directory is present, this operation

ddtrace/settings/_config.py

@@ -647,7 +647,8 @@ def __init__(self):
         self._llmobs_agentless_enabled = _get_config("DD_LLMOBS_AGENTLESS_ENABLED", None, asbool)
 
         self._inject_force = _get_config("DD_INJECT_FORCE", None, asbool)
-        self._lib_was_injected = False
+        # Telemetry for whether ssi instrumented an app is tracked by the `instrumentation_source` config
+        self._lib_was_injected = _get_config("_DD_PY_SSI_INJECT", False, asbool, report_telemetry=False)
         self._inject_enabled = _get_config("DD_INJECTION_ENABLED")
         self._inferred_proxy_services_enabled = _get_config("DD_TRACE_INFERRED_PROXY_SERVICES_ENABLED", False, asbool)
         self._trace_safe_instrumentation_enabled = _get_config("DD_TRACE_SAFE_INSTRUMENTATION_ENABLED", False, asbool)

lib-injection/sources/sitecustomize.py

@@ -373,10 +373,13 @@ def _inject():
         # Add the custom site-packages directory to the Python path to load the ddtrace package.
         sys.path.insert(-1, site_pkgs_path)
         _log("sys.path %s" % sys.path, level="debug")
+        # Used to track whether the ddtrace package was successfully injected. Must be set before importing ddtrace
+        os.environ["_DD_PY_SSI_INJECT"] = "1"
         try:
             import ddtrace  # noqa: F401
 
         except BaseException as e:
+            os.environ["_DD_PY_SSI_INJECT"] = "0"
             _log("failed to load ddtrace module: %s" % e, level="error")
             TELEMETRY_DATA.append(
                 create_count_metric(
@@ -429,10 +432,6 @@ def _inject():
                         ],
                     ),
                 )
-                # Track whether library injection was successful
-                ddtrace.config._lib_was_injected = True
-                os.environ["_DD_SSI_INJECT_SUCCESSFUL"] = "1"
-                ddtrace.internal.telemetry.telemetry_writer.add_configuration("instrumentation_source", "ssi", "code")
             except Exception as e:
                 TELEMETRY_DATA.append(
                     create_count_metric(