Add Supavisor pooler metrics to supabase integration

[gushecht]

What does this PR do?

Adds Supavisor pooler metrics to the Supabase integration's allowlist. Supabase Cloud's customer Metrics API (/customer/v1/privileged/metrics) exposes ~24 supavisor_* metrics from Supavisor's PromEx Tenant plugin, but none were mapped in metrics.py, so the scraper was silently dropping them.

This PR adds:

• Pool/connection gauges: supavisor.connections.active, supavisor.proxy.connections.active, supavisor.pool.connections.{checked_out,idle}, supavisor.tenants.active
• Throughput counters: supavisor.client.queries_count, supavisor.client.joins.{ok,fail}, supavisor.{client,db}.network.{recv,send}
• Lifecycle counters: supavisor.{client_handler,db_handler}.{started_count,stopped_count}, supavisor.db_handler.db_connection_count, supavisor.db_handler.prepared_statements_evicted_count
• Latency histograms: supavisor.pool.checkout.duration.{local,remote}, supavisor.client.query.duration, supavisor.client.connection.duration, supavisor.client.connection.lifetime_ms, supavisor.client_handler.state.duration

Fixture (tests/fixtures/privileged_metrics.txt), assertion list (tests/common.py), and metric documentation (metadata.csv) are updated to match.

Motivation

The most operationally useful Supavisor metric — supavisor_connections_active — backs the "Shared Pooler (Supavisor) Client Connections" graph in Supabase Studio's Observability section. It's the right metric to alert on pooler client-slot exhaustion, which is a common failure mode in serverless / Vercel Fluid Compute setups (e.g. supabase/discussions#40671) where pool sockets can leak across function terminations. Without these mappings, customers running the integration have no Datadog signal for this until the database starts rejecting connections.

Additional Notes

• Same gap exists in the SaaS supabase_cloud tile integration (no supabase.cloud.supavisor.* metrics ingested). Filing a separate ask with the saas-integrations team so that the SaaS scraper mirrors these mappings.
• Metric type/label data sourced from the canonical PromEx plugin in supabase/supavisor.

Review checklist (to be filled by the PR author)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ label attached
• If the PR doesn't need to be tested during QA, please add a qa/skip-qa label

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[chatgpt-codex-connector]

Rename changelog fragment to use numeric PR prefix

This fragment filename (+supavisor.added) will break changelog validation in PR CI, because ddev/src/ddev/utils/scripts/check_pr.py:get_core_repo_changelog_errors parses the part before the first . as an integer PR number (int(entry_pr_num)), which raises ValueError for +supavisor. In practice, any PR containing this file will fail the changelog check before review/release automation can proceed; the fragment should be renamed to <PR_NUMBER>.<type>.

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[gushecht]

[Claude on behalf of Gus] Already addressed — the next commit (156c5d3) renames +supavisor.added → 23749.added. Codex was reviewing the first commit only. The Check PR changelog workflow has since passed against the renamed fragment.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.04%. Comparing base (36bd36a) to head (156c5d3).
⚠️ Report is 28 commits behind head on master.

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