SPIKE: Investigate various document stores

Overview

We need a document store to store all the generated documents for each tenant
Explore various options and document pros and cons.
Note: The datastore must have proper opensource license(apache)
Few of them could be:
1. postgres
2. solr
3. elastic search
4. MongoDB
5. others

Few Areas to look at:
1. Ease of storage and retrieval
2. Ease of setup
3. backup and restore capabilities

Acceptance Criteria

• Various options are documented in FOLIO wiki
• The observations are presented to the team and a document store is selected
• Required user stories are created