Add prefix parameters to add docs and search

[vicilliar]

• Please check if the PR fulfills these requirements

• [x] 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)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Feature

• What is the current behavior? (You can also link to an open issue here) No prefix parameters in add documents or search functions

• What is the new behavior (if this is a feature change)?

• text_chunk_prefix added to add_documents

• text_query_prefix added to search

• textQueryPrefix added to SearchModel

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) No

• Other information: