Remove Parallel (Processes) in Marqo

[wanliAlex]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  remove Parallel processes in marqo

• What is the current behavior? (You can also link to an open issue here)
  we have a processes parameter in marqo add_or_replace_documents API that uses multiprocess to index documents.

• What is the new behavior (if this is a feature change)?
  We decide to remove the support of the multiprocess feature and remove the support of this parameter in the API, for the following reasons:

1. It blows out memory (it seems that loaded models are replicated for each process)

2. The (time) overhead from starting multiple processes makes it unviable for ~30 second HTTP requests. It only makes sense for much longer running requests (which is an unusual pattern for a REST API)

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  yes, this is a breaking change

• Have unit tests been run against this PR? (Has there also been any additional testing?)
  passes

• Related Python client changes (link commit/PR here)
  on going

• Related documentation changes (link commit/PR here)
  parameter processes has already been removed from the doc

• Other information:
  not

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added / updated (for bug fixes / features)