Add cli-subbcomands to mange users

ocis-accounts [list|delete|update|add|inspect]

Implements UpdateMask for the update request. Changed server-handler accordingly.
The commands use service-discovery to discover the backend.
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f