Fixes#1214Fixes#1231Fixes#1232
Implements `utils.ParseTagging` which is a generic implementation of parsing tags for both `PutObjectTagging` and `PutBucketTagging`.
- The actions now return `MalformedXML` if the provided request body is invalid.
- Adds validation to return `InvalidTag` if duplicate keys are present in tagging.
- For invalid tag keys, it creates a new error: `ErrInvalidTagKey`.