fix(gcp): refactor and improve GCP provider

[floreks]

Summary

• Refactored GCP provider
• Got rid of both direct gcloud calls from within the code and older google.golang.com SDK usage in favor of newer cloud.google.com SDK where applicable
• Refactored SDK clients usage to a standalone central client that is initialized once and can be reused for the lifecycle of a command call
• Added user info logs when using GCP provider to show basic information about current user
• Refactored kube config setup logic to only use SDK instead of gcloud to manually assemble and merge new entry into the local kubeconfig file
• Extracted user-provided input gathering to InputProvider interface so that survey can be easily replaced later on
• Improved initial credentials check and error message when ADC is not properly configured

Labels

Test Plan

Locally w/ plural up

Checklist

• If required, I have updated the Plural documentation accordingly.
• I have added tests to cover my changes.
• I have added a meaningful title and summary to convey the impact of this PR to a user.
• I have added relevant labels to this PR to help with categorization for release notes.

[linear]

PROD-3962 gcp failed auth error messages stink

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	golang.org/​x/​oauth2@​v0.29.0 ⏵ v0.32.0	+1
	golang.org/​x/​crypto@​v0.37.0 ⏵ v0.43.0	+1
	google.golang.org/​grpc@​v1.72.0 ⏵ v1.76.0	+1
	cloud.google.com/​go/​compute@​v1.37.0 ⏵ v1.49.1	+2				-20
	google.golang.org/​genproto@​v0.0.0-20250428153025-10db94c68c34 ⏵ v0.0.0-20250603155806-513f23925822	+1
	golang.org/​x/​text@​v0.24.0 ⏵ v0.30.0	+1
	google.golang.org/​api@​v0.231.0 ⏵ v0.254.0	+1
	cloud.google.com/​go/​storage@​v1.52.0 ⏵ v1.57.1	-2
	cloud.google.com/​go/​resourcemanager@​v1.10.6 ⏵ v1.10.7	+1
	cloud.google.com/​go/​serviceusage@​v1.9.6 ⏵ v1.9.7	+1
	cloud.google.com/​go/​container@​v1.42.4 ⏵ v1.43.0	+1
	golang.org/​x/​term@​v0.31.0 ⏵ v0.36.0	+1

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