Add an optional postgres for the catalog, initialized on first use

[ZohebShaikh]

Stacked on #11.

Adds an opt-in postgres (postgresql.enabled, off by default) holding one catalog database shared by every beamline. The postgres image creates the database on first start, and each tiled pod gets an init-catalog init container that runs tiled catalog init --if-not-exists, retrying until postgres is up or while another beamline's pod is initializing it.

The tiled pods get PGHOST, PGUSER, PGPASSWORD and PGDATABASE. To use the bundled postgres, set the tree's uri to postgresql://$PGUSER:$PGPASSWORD@$PGHOST/$PGDATABASE in place of the default sqlite one. The password comes from tiled-secrets key POSTGRES_PASSWORD, and must be URL-safe.

Instructions to reviewer on how to test:

1. helm lint Charts/tiled --set postgresql.enabled=true
2. helm template r Charts/tiled --set postgresql.enabled=true and confirm a postgres StatefulSet and Service, and an init-catalog init container on each beamline Deployment
3. Confirm nothing changes in the render with postgresql.enabled=false

Checks for reviewer

• Would the PR title make sense to a user on a set of release notes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.64%. Comparing base (f09a113) to head (77ddc5c).

Additional details and impacted files

@@             Coverage Diff              @@
##           envoy-proxy      #21   +/-   ##
============================================
  Coverage        61.64%   61.64%           
============================================
  Files                3        3           
  Lines              219      219           
============================================
  Hits               135      135           
  Misses              84       84           

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