Merge branch 'agent-impersonation-env-tier-docs' into 'master'

Add environment tier to agent impersonation docs

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/100677



Merged-by: Phillip Wells <pwells@gitlab.com>
Approved-by: Mikhail Mazurskiy <mmazurskiy@gitlab.com>
Approved-by: Phillip Wells <pwells@gitlab.com>
Co-authored-by: Tiger <twatson@gitlab.com>