Follow-up from "Pass configurable file size limit to gitlab-elasticsearch-indexer"

The following discussion from !84 (merged) should be addressed:

• @mbergeron started a discussion: (+2 comments)

  I think we could embed the Encoder type in the Indexer type, as it is required by the Indexer type.

  This would remove a couple references to encoder from within the Indexer functions, as all the methods of Encoder will be available directly on the Indexer — actually all Indexer would the be an Encoder.

  Side note here, I just want to point out that even if we embed Submitter we are not leveraging the type embedding in Indexer functions. We should do that, but not now.