Entry content-type and aws s3 user metadata

[nopcoder]

Fix #2296
Fix #2429

1. ContentType added to entry metadata:
   S3 gateway multipart upload and put object can pass content-type header and it will be returned as part of the entry metadata and get object content-type. Object head request will report the content type as S3 does.
   OpenAPI's link object, stage, and upload accept content-type and store them as part of the object metadata.
   Link physical object API call was updated to return the object stats in order to identify the content-type the server set in case we didn't pass any. We kept the same status code in order not to break backward compatibility.
   lakectl upload was added a '--content-type' flag to support setting value while uploading the file.
2. AWS S3 user-metadata passed as x-amz-meta-*.
   S3 gateway will pass the headers as the entry metadata fields and return all metadata with x-amz-meta- prefix as headers on getting object request
   No changes were introduced to our OpenAPI - didn't add new functionality to get/set the object metadata in this PR.
3. Graveler identity will consider object content-type as part of the object identity.

Future work will include testing this feature.

[arielshaqed]

Neat, thanks!

This is really good stuff; the only required changes are to the DDL update filenames, which AFAICT need to say "35" not "34" :-/

[nopcoder]

Neat, thanks!

This is really good stuff; the only required changes are to the DDL update filenames, which AFAICT need to say "35" not "34" :-/

was late to the party, your PR took it ;)

[arielshaqed]

Great, thanks!