feat: Adds GCP Secret Manager trigger authentication docs

[neelanjan00]

A description of what has been changed

• Adds GCP Secret Manager trigger authentication docs

Checklist

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[wozniakjan]

looks pretty good, just a couple of nits from my side.
Also the PR title should not be chore but feat, can you please change that?

[wozniakjan]

@neelanjan00 regarding the failing jobs, I think you will need to adjust .htmltest like in e03ee09

[zroubalik]

@neelanjan00 please also add this page here to the list, to fix netlify issues:

keda-docs/.htmltest.yml

Line 8 in 02d6f01

- /docs/2.12/authentication-providers/configmap/

See this PR for a reference: https://github.com/kedacore/keda-docs/pull/1289/files

[neelanjan00]

Thank you for the detailed reveiw, @wozniakjan @zroubalik. PTAL.

[wozniakjan]

lgtm