This change adds a `Secret` property to `HelpKV` to identify secrets
like passwords and auth tokens that should not be revealed by the server
in its configuration fetching APIs. Configuration reporting APIs now do
not return secrets.
- This change renames the OPA integration as Access Management Plugin - there is
nothing specific to OPA in the integration, it is just a webhook.
- OPA configuration is automatically migrated to Access Management Plugin and
OPA specific configuration is marked as deprecated.
- OPA doc is updated and moved.
This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`
