rgw/crypt - improve PutBucketEncryption / RGWBucketEncryptionConfig

rgw/crypt - improve PutBucketEncryption / RGWBucketEncryptionConfig

The existing logic for bucket encryption was incomplete.  This adds the
rest of the changes necessary to support sse-kms with default bucket
encryption.

The new logic has these changes:

on input: SSEAlgorithm is now optional.

On output: emit xmlns attribute at top level.
also output
BucketKeyEnabled and KMSMasterKeyID.
Hnadle "empty rule" case.

for testing and diagnostics:
support RGWBucketEncryptionConfig in ceph-dencoder

Signed-off-by: Marcus Watts <mwatts@redhat.com>
src/rgw/rgw_bucket_encryption.cc
src/rgw/rgw_bucket_encryption.h
src/rgw/rgw_crypt.cc
src/rgw/rgw_dencoder.cc
src/rgw/rgw_json_enc.cc
src/rgw/rgw_rest_s3.cc
src/tools/ceph-dencoder/rgw_types.h