Use redis to cache results

[EDsCODE]

Changes

implements #765 and #940

• added a decorator you can use on functions that you want to cache
• trends/funnel queries will be cached for 30 seconds by default (so that repeat visits don't keep recalculating queries)
• clicking save funnel will force a refresh so you don't have stale metrics when you're trying to update the funnel
• dashboard items will be cached for 15 minutes and worker will check for all cached dashboard items and refresh every 10 minutes. this should keep the cache perpetually updated
• refactor remaining dashboard elements to use hooks and kea (funnel, pie, table)

Todo:

• keep cache up to date with worker
• delete cached item when dashboard item is deleted
• make sure all items are cached properly (pie graph, line graph, table, funnel)
• make sure last updated prompt is updated on click and looks readable
  - [ ] dashboard items out of order after refresh

Checklist

• All querysets/queries filter by Team (if applicable)
• Backend tests (if applicable)
• Cypress E2E tests (if applicable)

[EDsCODE]

I moved everything out of the class because I needed the logic to be easily reusable by the worker

[EDsCODE]

reusing the redis we use for everything else. may consider having a dedicated instance because we are likely going to end up caching 100s -> 1000s of dashboard items indefinitely

[EDsCODE]

somewhat inflexible decorator for the moment. adding this decorator to an endpoint will require an explicit condition to handle

[EDsCODE]

One thing to note is that if we have a default expiry of 30 seconds this will be nice for very heavily trafficked instances but for new instances, it might seem like the data is not refreshing/stuck when you're on the trends page. I'm open to limiting the caching for dashboart items only

[timgl]

I love it. Some small comments.