[backend] fix(multi-tenancy): migration 5_06 without alter database (#4864)

[corinnekrych]

Proposed changes

Pre-release is failing to run v5_06 migration due to privilege for "ALTER DATABASE".
This PR propose an alternative which required less privileges.

Testing Instructions

1. Step-by-step how to test
2. Environment or config notes

Related issues

• Closes #ISSUE-NUMBER

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality
• For bug fix -> I implemented a test that covers the bug

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[Copilot]

Pull request overview

This PR adjusts Flyway migration V5_06__Enable_row_level_security to avoid requiring ALTER DATABASE privileges during pre-release deployments by switching the default app.current_tenant initialization from a database-level setting to a role-level setting.

Changes:

• Replaces ALTER DATABASE ... SET app.current_tenant = ... with ALTER ROLE ... SET app.current_tenant = ... in the V5_06 migration.
• Removes database name lookup (getCatalog()) since the migration no longer issues ALTER DATABASE.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.40%. Comparing base (d3c8444) to head (2d75908).

Additional details and impacted files

@@                  Coverage Diff                  @@
##             release/current    #5690      +/-   ##
=====================================================
- Coverage              40.40%   40.40%   -0.01%     
  Complexity              6112     6112              
=====================================================
  Files                   2123     2123              
  Lines                  56998    56997       -1     
  Branches                7230     7230              
=====================================================
- Hits                   23031    23030       -1     
  Misses                 32611    32611              
  Partials                1356     1356              

Flag	Coverage Δ
backend	64.34% <100.00%> (-0.01%)	⬇️
frontend	1.42% <ø> (ø)

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