Add find_matching_sessions function to enable keyword searching across sessions, based on metadata

[nonprofittechy]

Adds a new function, find_matching_sessions, which can be used to search and retrieve a set of matching sessions across all unencrypted interview sessions on a server.

The expected use case is for an attorney or other advocate to be able to search through their own sessions to find a document they automated for a particular user. It can also be used in a scenario where there is a generic "intake" interview that the attorney wants to use as a starting point to automate future documents with. Search results can be limited to a particular interview or set of interviews, such as an intake questionnaire.

Searching across sessions that you did not create or were not explicitly shared is limited to 3 user roles by default: admin, developer, and advocate.

Matching is performed entirely based on keywords in the jsonstorage table; by default, only ones with the metadata key name set to "metadata." If your interview uses the Assembly Line, it automatically saves the name of the users and other_parties lists to the jsonstorage table with this key on each screen load.

Example:

matching_sessions=find_matching_sessions("smith", user_id="all", filenames=[f"{user_info().package}:intake.yml", "docassemble.MyPackage:intake.yml"])

[samglover]

Looks good to me!