Multiple filters on the frontend

[macobo]

Changes

This PR does a few things:

• It adds a new multiple_filters feature flag which allows adding multiple filters on the frontend (except for goals).
• Updates filter serialization on the frontend
• Adds new filter (and query) parsing methods (for a follow-up PR)
• Reduces number of internal filter operators we support, collapsing list and single-item operators

Blocked on #4118 - will update filtering within after that PR lands.

Tests

• Automated tests have been added
• This PR does not require tests

Changelog

• Entry has been added to changelog
• This PR does not make a user-facing change

Documentation

• Docs have been updated
• This change does not need a documentation update

Dark mode

• The UI has been tested both in dark and light mode
• This PR does not change the UI

[ukutaht]

Approved but I would like to discuss which filter types will be available to the client

[ukutaht]

This seems to go in the direction that matches is a first-class operation that would also be available in the API. Am I reading it right?

My thinking on what filters should be available to client:

• is - can deal with lists like you've already done in this PR. Can also take wildcards.
• contains - equivalent to is where value is wrapped with *${value}*

I'm not sure about exposing matches for simple wildcards. It would fit better for a full regex match filter operation in the future.

WDYT?

[macobo]

Not sure I completely understood. Created https://3.basecamp.com/5308029/buckets/37310803/card_tables/cards/7494308360 for this discussion so it doesn't get dropped.