migrate from Bootstrap 4 to Bootstrap 5

[jrochkind]

it's going to be very painful to migrate, especially since problems are not generally going ot be caught by automated testing.

But Bootstrap 4 is End-of-life. https://getbootstrap.com/docs/4.6/end-of-life/

And at some point possibly soon will not work with latest Blacklight releases either.

It looks like Blacklight 7.x that we currently use does NOT support Bootstrap 5. That makes upgrading even more complciated, as we'd need a a release that jumps to Blacklight 8 (already has some blockers for us including non-support for blacklight_range_limit_) at the same time it switches from Bootstrap 4 to 5. It's going to be rough.

[jrochkind]

Hm, actually Blacklight 7 may support Bootstrap 5? https://github.com/projectblacklight/blacklight/blob/release-7.x/.github/workflows/ruby.yml#L51