add a maintainance command overview

[Svanvith]

No description provided.

[v-scharf]

cli commands:

• removes all the file versions: opencloud revisions purge

• check opencloud version: opencloud version

• search index: opencloud search index --all-spaces

• check backup consistency: opencloud backup consistency
  not sure about opencloud benchmark client has a panic and opencloud benchmark syscalls need ask @rhafer

• admin reset password: idm resetpassword

• create app tokens: auth-app create --user-name=$user --expiration=$expirationTime