Add search by book subject/subject_places

[ilkka-ollakka]

Description

Add search by subjects/subject_places, all connectors do seem to map that data.

This might need adding index to Edition.subjects and Edition.subject_places in database?

• Related Issue #
• Closes #

What type of Pull Request is this?

• Bug Fix
• Enhancement
• Plumbing / Internals / Dependencies
• Refactor

Does this PR change settings or dependencies, or break something?

• This PR changes or adds default settings, configuration, or .env values
• This PR changes or adds dependencies
• This PR introduces other breaking changes

Details of breaking or configuration changes (if any of above checked)

Documentation

• New or amended documentation will be required if this PR is merged
• I have created a matching pull request in the Documentation repository
• I intend to create a matching pull request in the Documentation repository after this PR is merged

Tests

• My changes do not need new tests
• All tests I have added are passing
• I have written tests but need help to make them pass
• I have not written tests and need help to write them

[ilkka-ollakka]

I'm not sure if this approach is feasible, or should the subjects/subject_places filtering be added to regular book search, or some other approach. I just wanted this out there to get opinions.