Refactor: Eligibility start page

[thekaveman]

Supersedes #1488 -- ultimately moved away from Django template tags in favor of our trusty includes.

Stole some ideas from #1489

Part of #1442

Closes #1477

Goals

• Move as much copy as possible away from the database (models), towards the templates
• Reduce or eliminate the reliance on view model classes
• Change incrementally, don't break existing pages/flows
• Address the points in this comment: Refactor usage of view models #1442 (comment)

Overview

1. Add field on EligibilityVerifier to reference a custom template for Start page
2. Create 3 customized Start templates extending eligibility/start.html
   • eligibility/start__login_gov.html
   • eligibility/start__mst_courtesy_card.html
   • eligibility/start__veteran.html
3. Move corresponding copy from model fields into customized template files
4. Change eligibility:start view to use the verifier's template

[machikoyasuda]

LGTM!

I tried editing the start.html file (removing the whole help-text section) to see how the includes would respond and it worked perfectly + quickly (the whole section should be removed, even if the includes calls for it). Sticking with the trusty includes has led to code that's easier for me to read - no more djLint on/off switches - and more plain HTML/regular includes block overrides.

One change request: I believe the secondary_details code I wrote last Sprint can be deleted:

• remove parameter from MediaItem view model
• remove from media-list.html template

The base branch was changed.

[thekaveman]

Rebased on the changes in #1489

EDIT: as y'all were merging that one and approving this one 🤣

[thekaveman]

Let's get #1499 and #1501 in first since those are simpler, it would be more challenging to rebase/deal with conflicts in both of them against this branch.

[angela-tran]

This is looking really good so far!

[thekaveman]

Ready for re-review.

I couldn't fully get rid of the tag work from #1488, but I tried to squash it down to a few logical commits for the structure, and one big refactor for the includes.

Thanks for all the comments on the earlier PR, and the radio buttons PR, that all helped clarify a better way forward.

[angela-tran]

I've read through the code changes and run the app locally. This refactor looks great!! 💯