Enhance policy handling to support SSE and WORM (#5790)

- 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.

cmd/xl-v1.go

@@ -43,9 +43,6 @@ type xlObjects struct {
 	// Byte pools used for temporary i/o buffers.
 	bp *bpool.BytePoolCap
 
-	// Variable represents bucket policies in memory.
-	bucketPolicies *bucketPolicies
-
 	// TODO: Deprecated only kept here for tests, should be removed in future.
 	storageDisks []StorageAPI