Update PostgreSQL volume mount paths for PostgreSQL 18

[Copilot]

What

Updated volume mount paths from /var/lib/postgresql/data to /var/lib/postgresql in all Docker Compose files.

Why

PostgreSQL 18 changed the Docker image to use version-specific PGDATA (/var/lib/postgresql/18/docker) and moved the VOLUME directive to /var/lib/postgresql. Mounting at the parent directory enables pg_upgrade --link for faster major version upgrades.

Reference: https://hub.docker.com/_/postgres#pgdata

Additional info (optional)

Changed files:

• compose_example.yml
• compose.local-db.yml
• packages/backend/test-federation/compose.a.yml
• packages/backend/test-federation/compose.b.yml

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

Original prompt

---

This section details on the original issue you should resolve

<issue_title>postgresコンテナのvolumeのマウントパス変更が必要</issue_title>
<issue_description>#16850 で PostgreSQL 18 を使うようになりましたが、これに伴い compose_example.yml などに記述している postgres コンテナの volume のマウントパスを、 /var/lib/postgresql/data から /var/lib/postgresql へ変更する必要がありそうです。

参考：https://hub.docker.com/_/postgres#pgdata

Important Change: the PGDATA environment variable of the image was changed to be version specific in PostgreSQL 18 and above. For 18 it is /var/lib/postgresql/18/docker. Later versions will replace 18 with their respective major version (e.g., /var/lib/postgresql/19/docker for PostgreSQL 19.x). The defined VOLUME was changed in 18 and above to /var/lib/postgresql. Mounts and volumes should be targeted at the updated location. This will allow users upgrading between PostgreSQL major releases to use the faster --link when running pg_upgrade and mounting /var/lib/postgresql.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes postgresコンテナのvolumeのマウントパス変更が必要 #16949

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.83%. Comparing base (e0b872d) to head (8029e4c).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #16986   +/-   ##
========================================
  Coverage    62.83%   62.83%           
========================================
  Files         1150     1150           
  Lines       115228   115228           
  Branches      7892     7894    +2     
========================================
+ Hits         72400    72407    +7     
+ Misses       40668    40661    -7     
  Partials      2160     2160           

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