[processor/resourcedetection] Add a note about missing host.name in GKE workload identity

[songy23]

Description:
Add a note about GKE resource detector missing host.name in GKE workload identity. Context: #10486, #12355 and #15716

Link to tracking Issue:
Fixes #15716

Testing:

Documentation:

[songy23]

cc @dashpole @mx-psi @gbbr

[songy23]

Please add label skip changelog

[runforesight]

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 build-and-test workflow has finished in 7 minutes 37 seconds (42 minutes 23 seconds less than main branch avg.) and finished at 29th Mar, 2023.

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Job	Failed Steps	Tests
integration-tests	N/A	N/A	See Details

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