refactor: Standardize WAL-G config inclusion

[hunleyd]

depends on #1956

- WAL-G configuration is now managed by placing `wal-g.conf` in `/etc/postgresql-custom/conf.d/`.
- This aligns with PostgreSQL's standard practice of including configuration files from `conf.d` subdirectories.
- Direct inclusion of `wal-g.conf` in `postgresql.conf` has been removed.
- PostgreSQL `archive_mode` is now explicitly set to `on` with a no-op `archive_command` in `postgresql.conf.j2`.

✅ docker build
✅ flake check

[Copilot]

Pull request overview

This PR refactors WAL-G configuration management to follow PostgreSQL's standard practice of including configuration files from conf.d subdirectories, rather than explicitly including wal-g.conf in postgresql.conf.

Key changes:

• WAL-G configuration now resides in /etc/postgresql-custom/conf.d/wal-g.conf instead of /etc/postgresql-custom/wal-g.conf
• PostgreSQL archive_mode and archive_command are now explicitly set in the main configuration file with a no-op command
• Direct inclusion of wal-g.conf in postgresql.conf has been removed

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ansible/tasks/setup-wal-g.yml	Updates WAL-G config deployment to use conf.d directory and removes explicit inclusion logic
ansible/files/postgresql_config/postgresql.conf.j2	Adds explicit archive_mode = on and no-op archive_command, removes WAL-G include directive
ansible/files/postgresql_config/conf.d/wal-g.conf	Reorganizes configuration settings and removes redundant archive_mode declaration
Dockerfile-orioledb-17	Removes WAL-G config copy and inclusion sed command
Dockerfile-17	Removes WAL-G config copy and inclusion sed command
Dockerfile-15	Removes WAL-G config copy and inclusion sed command

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