Merge branch 'eduardosanz/gc-iam-improvements-4' into 'master'

Update Google Cloud IAM manual setup instructions

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/148209



Merged-by: Paul Gascou-Vaillancourt <pgascouvaillancourt@gitlab.com>
Approved-by: Fiona Neill <fneill@gitlab.com>
Approved-by: Pedro Moreira da Silva <hi@pedroms.com>
Approved-by: Ravi Kumar <rkumar@gitlab.com>
Approved-by: Paul Gascou-Vaillancourt <pgascouvaillancourt@gitlab.com>
Reviewed-by: Pedro Moreira da Silva <hi@pedroms.com>
Reviewed-by: Paul Gascou-Vaillancourt <pgascouvaillancourt@gitlab.com>
Reviewed-by: Justin Ho Tuan Duong <hduong@gitlab.com>
Reviewed-by: Eduardo Sanz García <esanz-garcia@gitlab.com>
Co-authored-by: Eduardo Sanz García <esanz-garcia@gitlab.com>