robustness: implement cluster client endpoint switching

[henrybear327]

Introduce optional cluster client endpoint switching.

This would allow us to test out the client reconnection behaviors, such as the resumable guarantee for watches.

Used in #21472

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.43%. Comparing base (50f4ea2) to head (62787b8).
⚠️ Report is 31 commits behind head on main.

Additional details and impacted files

see 27 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #21471      +/-   ##
==========================================
- Coverage   68.47%   68.43%   -0.04%     
==========================================
  Files         428      428              
  Lines       35291    35291              
==========================================
- Hits        24165    24152      -13     
- Misses       9730     9738       +8     
- Partials     1396     1401       +5     

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[henrybear327]

/retest

[henrybear327]

Not sure if this is a better idea than treating 0 as "don't switch".

[henrybear327]

/retest

[serathius]

Can you describe the solution, how it works, what purpose it serve, what are alternatives?