feat(document-search,cli): add command to ingest document

[mhordynski]

Feature description

A new command should allow users to interactively add a new document to a DocumentSearch instance.

ragbits document-search ingest gcs://my_bucket/my_file.txt
ragbits document-search ingest gcs://my_bucket/*

Ways to select DocumentSearch: enabled by #223 - do it in similar fashion as with VectorStore selection.

Motivation

Ingesting documents is a very common operation in the early stages of project development; therefore, a CLI utility may be heavily used by developers.

Additional context

Enabled by: #221 to parse string values to sources.
Enabled by: #223 to have baseline how to select DocumentSearch.