fix: update API endpoints for RustFS compatibility to fix 501 NotImplemented errors

[yxrxy]

fix: #6

Fixes:

• Policy create: POST → PUT
• Policy attach: /set-policy → /set-user-or-group-policy with query params
• Group add: use update-group-members
• Group add/rm-members: add groupStatus field
• Service account create: /add-service-account → /add-service-accounts, add required expiry param
• Service account delete: /delete-service-account → /delete-service-accounts
• Service account info: make accessKey optional