Document Shibboleth Metadata Admin app

Needs updating to new template and deployment updated.

Part of: https://gitlab.developers.cam.ac.uk/uis/devops/admin/-/issues/205

changed milestone to %DevOps Sprint 121

added placeholder workflowIn Progress labels

mentioned in merge request !81 (merged)

added 2h of time spent at 2021-05-20

added workflowReview Required label and removed workflowIn Progress label

mentioned in commit 829ae987

closed with merge request !81 (merged)