Merge branch 'bastirehm-mention-service-ping-api-in-docs' into 'master'

Add mention of service ping API in docs for Service Ping

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/154394



Merged-by: Lorena Ciutacu <lciutacu@gitlab.com>
Approved-by: Lorena Ciutacu <lciutacu@gitlab.com>
Reviewed-by: Lorena Ciutacu <lciutacu@gitlab.com>
Co-authored-by: Sebastian Rehm <srehm@gitlab.com>