This PR fixes a regression where the remote bucket policies
were not updated due to policy.Resource not having exported
fields, gob fails with unexported fields while marshalling.
Previously we used allow bucket policies without
`Version` field to be set to any given value, but
this behavior is inconsistent with AWS S3.
PR #5790 addressed this by making bucket policies
stricter and cleaner, but this causes a breaking
change causing any existing policies perhaps without
`Version` field or the field to be empty to fail upon
server startup.
This PR brings a code to migrate under these scenarios
as a one time operation.
- remove old bucket policy handling
- add new policy handling
- add new policy handling unit tests
This patch brings support to bucket policy to have more control not
limiting to anonymous. Bucket owner controls to allow/deny any rest
API.
For example server side encryption can be controlled by allowing
PUT/GET objects with encryptions including bucket owner.
