[DPE-9630] fix: safe pgdata symlink setup with accurate status reporting

[marceloneppel]

Issue

During pgdata symlink setup, rm -rf was used to remove /var/lib/postgresql/16/main if it existed as a non-symlink. This could cause data loss if the directory unexpectedly contained data. Additionally, the charm set ActiveStatus while PostgreSQL was still in Patroni's "starting" state (not yet accepting connections), causing tests and consumers waiting for all_active to proceed prematurely.

Solution

Replace rm -rf with mv to persistent storage (DPE-9630)

Patroni's remove_data_directory() can delete the pgdata symlink during failed pg_basebackup retries, and the retry recreates the path as a real directory. Since ln -sfn cannot replace a real directory, the charm now checks with test -L and moves the directory to PV-backed storage (pgdata-backup-<timestamp>) instead of deleting it, preserving data for debugging.

Show WaitingStatus when PostgreSQL is starting

When Patroni reports member_started=True but the health state is "starting" (PostgreSQL not yet accepting connections), _set_active_status now sets WaitingStatus("waiting for PostgreSQL to start") instead of ActiveStatus. This prevents premature readiness signaling. The WaitingStatus is:

• Skipped during refresh (so the refresh library doesn't consider the unit unhealthy)
• Exempted from the _on_update_status early exit (so update-status can re-evaluate and set ActiveStatus once PostgreSQL finishes starting)

Add all_active waits to async replication tests

test_data_replication and test_standby_promotion lacked all_active waits before querying units, causing Connection refused errors when PostgreSQL was still starting.

Checklist

• I have added or updated any relevant documentation.
• I have cleaned any remaining cloud resources from my accounts.

[codecov]

Codecov Report

❌ Patch coverage is 58.33333% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.61%. Comparing base (b4e70ef) to head (2fff5c7).

Files with missing lines	Patch %	Lines
src/charm.py	58.33%	5 Missing ⚠️

❌ Your project check has failed because the head coverage (68.61%) is below the target coverage (70.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##           16/edge    #1359      +/-   ##
===========================================
- Coverage    68.64%   68.61%   -0.03%     
===========================================
  Files           16       16              
  Lines         3881     3891      +10     
  Branches       590      592       +2     
===========================================
+ Hits          2664     2670       +6     
- Misses        1009     1014       +5     
+ Partials       208      207       -1     

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