Add executionClusterLabel

[RRap0so]

Tracking issue

Closes #5395

Why are the changes needed?

To add flytectlthe ability to select what execution it should go to.

What changes were proposed in this pull request?

Add a new field in the execution spec.

How was this patch tested?

With a unit test

• [x] I updated the documentation accordingly.
• [x] All new and existing tests passed.
• [x] All commits are signed-off.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 61.11%. Comparing base (d04cf66) to head (bc3ba3e). Report is 132 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5394   +/-   ##
=======================================
  Coverage   61.10%   61.11%           
=======================================
  Files         793      793           
  Lines       51164    51169    +5     
=======================================
+ Hits        31265    31270    +5     
  Misses      17027    17027           
  Partials     2872     2872           

Flag	Coverage Δ
unittests-datacatalog	69.31% <ø> (ø)
unittests-flyteadmin	58.90% <ø> (ø)
unittests-flytecopilot	17.79% <ø> (ø)
unittests-flytectl	68.34% <100.00%> (+0.02%)	:arrow_up:
unittests-flyteidl	79.30% <ø> (ø)
unittests-flyteplugins	61.94% <ø> (ø)
unittests-flytepropeller	57.32% <ø> (ø)
unittests-flytestdlib	65.82% <ø> (ø)

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[eapolinario]

docs failures are unrelated, the fix for that being https://github.com/flyteorg/flyte/pull/5425.