fix(kuma-cp): add cp selector to global sync service

[jakubdyszkiewicz]

Summary

CP selector in Global Remote Sync service was missing.
It was ok, because in Global CP was the only component that was running with app.kubernetes.io/name: kuma, so it was always selected, but we should select the control plane explicitly in case a new component will arrive in the future next to Global CP.

Issues resolved

No reported issues.

Documentation

No docs.

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• Update UPGRADE.md with any steps users will need to take
  when upgrading.
• Add backport-to-stable label if the code is backwards compatible. Otherwise, list breaking changes.

[codecov-commenter]

Codecov Report

Merging #3579 (12e2e7c) into master (dfb2ade) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3579   +/-   ##
=======================================
  Coverage   51.57%   51.58%           
=======================================
  Files         918      918           
  Lines       55568    55568           
=======================================
+ Hits        28657    28662    +5     
+ Misses      24625    24623    -2     
+ Partials     2286     2283    -3     

Impacted Files	Coverage Δ
pkg/plugins/leader/postgres/leader_elector.go	97.87% <0.00%> (-2.13%)	⬇️
pkg/xds/generator/direct_access_proxy_generator.go	85.86% <0.00%> (-1.09%)	⬇️
api/observability/v1/mads.pb.go	35.56% <0.00%> (+1.03%)	⬆️
pkg/mads/v1/client/client.go	43.75% <0.00%> (+2.50%)	⬆️
pkg/xds/cache/once/once.go	100.00% <0.00%> (+5.00%)	⬆️
pkg/xds/cache/once/cache.go	87.17% <0.00%> (+5.12%)	⬆️

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