Use a redis based session store

[eanders]

Please squash merge this PR

Description

This moves from a cookie session store to a redis session store. Of note:

1. Sessions are capped at 12 hours (by the config)
2. Sessions are not removed by calling Rails.cache.clear, which is good
3. Sessions can be invalidated from the admin Sessions page
4. Deploying this change WILL invalidate all logged in users, so it should be done off hours

Type of change

• [x] New feature (adds functionality)

Checklist before requesting review

• [x] I have performed a self-review of my code
• [x] I have run the code that is being changed under ideal conditions, and it doesn't fail
• [x] My code includes comments and/or descriptive variable names to help other engineers understand the intent (or not applicable)
• [x] My code follows the style guidelines of this project (rubocop)
• [x] I have updated the documentation (or not applicable)
• [x] If it's not obvious how to test this change, I have provided testing instructions in this PR or the related issue

[gigxz]

I'm getting authentication error failures on the graphql tests locally for this branch @eanders. Those tests use LoginAndPermissionsSpecHelper. Let me know if you want me to poke at those (and the HMIS System Tests), happy to take a look!