This PR brings several QoL changes to how the metadata can be requested.

1. Query metadata will always include UUID. Deleted Metadata.UUID to avoid suggesting that returning it is optional.
2. Metadata.ALL is a shorthand for including all metadata fields.
3. Method .includeVector() as a shorthand for .returnMetadata(Metadata.VECTOR) to mimic a similar functionality in the other clients

This should also fix an issue where Pagination could continue to run forever when any metadata was requested explicitly.

// We previously had a check like:
//   if (returnMetadata.isEmpty()) returnMetadata.add(Metadata.UUID);
// Which meant that query below never gets a UUID from a server.
// Because the "last UUID" is null in this case we always try to fetch the first page
// and never advance the cursor.
things.paginate(p -> p.returnMetadata(Metadata.CREATION_TIME_UNIX)).forEach(...);

Always including the object's UUID addressed that bug.