PMM-15240: enable All on Cluster filter in PostgreSQL Replication Overview

[mattiasimonato]

Ticket number: PMM-15240

Feature build: SUBMODULES-4505

• Enable includeAll on the Cluster template variable and default it to All.
• Stops the dashboard from being locked to one Patroni cluster so standalone (non-Patroni) PostgreSQL nodes can appear in Node Name / Service Name and replication panels.

Summary by CodeRabbit

• New Features
  • The PostgreSQL Replication Overview dashboard now supports viewing data for all clusters by default.
  • Added the ability to select all clusters from the dashboard filter.

[coderabbitai]

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly states that the Cluster filter now supports the All option in the PostgreSQL Replication Overview dashboard.
Description check	✅ Passed	The description includes the required ticket and feature build fields and clearly explains the dashboard change and its purpose.

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_{Comment @coderabbitai help to get the list of available commands.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.03%. Comparing base (31318c7) to head (ed7deb6).
⚠️ Report is 91 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5727      +/-   ##
==========================================
- Coverage   43.59%   37.03%   -6.56%     
==========================================
  Files         415      215     -200     
  Lines       43134     7168   -35966     
  Branches        0      585     +585     
==========================================
- Hits        18804     2655   -16149     
+ Misses      22454     4317   -18137     
+ Partials     1876      196    -1680     

Flag	Coverage Δ
admin	34.96% <ø> (+0.17%)	⬆️
agent	?
managed	?
unittests	41.29% <ø> (?)
vmproxy	?

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