fix: preserve unix DogStatsD URLs in Gunicorn config

[hshree-cs]

Finishes GSRE-3388

Updates Gunicorn StatsD configuration to preserve unix:// DogStatsD URLs.This prevents invalid socket configuration when DD_DOGSTATSD_URL is set to a Unix socket path and should resolve StatsD transport errors caused by the previous parsing logic

Merge checklist:
Check off if complete or not applicable:

• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

Post-merge:

• Backported to latest and next named releases

[Copilot]

Pull request overview

Updates the Gunicorn configuration used by commerce-coordinator to better handle Datadog DogStatsD endpoint configuration, specifically preserving unix://... URLs when DD_DOGSTATSD_URL points at a Unix domain socket.

Changes:

• Adds explicit handling for DD_DOGSTATSD_URL values starting with unix:// so the socket URL is passed through as-is.
• Retains existing behavior for udp://... endpoints by stripping the scheme to match Gunicorn’s expected HOST:PORT format.

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[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (1)

commerce_coordinator/docker_gunicorn_configuration.py:21

• The unix-socket branch only treats the exact string "unix://" as invalid, but values like "unix:///" (no path) or "unix://path" (missing the third slash) would still be forwarded to Gunicorn even though the comment says the expected form is "unix:///path". Consider normalizing/validating the URL so you only set statsd_host when a non-empty socket path is present, and rewrite "unix://" to "unix:///" for consistency.

    if _dogstatsd_url.startswith("unix://"):
        # Gunicorn accepts unix socket directly as "unix:///path".
        _statsd_host = _dogstatsd_url if _dogstatsd_url != "unix://" else ""
    else: