Update to Bootstrap 5

[corylown]

Work in progress here: main...bootstrap5

Depends on:

• New release of Spotlight with projectblacklight/spotlight@b0873d3
• Updating bootstrap_form to ~> 5.4 in Exhibits

Gotchas: blacklight_range_limit does not work with Bootstrap 5:

• Support Bootstrap 5 projectblacklight/blacklight_range_limit#177
• asset generator fails on Blacklight 8 projectblacklight/blacklight_range_limit#210
• Bootstrap 5 javascript compatibility projectblacklight/blacklight_range_limit#212
• Blacklight.modal is undefined when using Blacklight 8 projectblacklight/blacklight_range_limit#231

There are accessibility concerns with blacklight_range_limit anyway, and based on discussions with @caaster a more limited date facet UI may be acceptable. Here's what we did for stanford-arclight for now:
sul-dlss/stanford-arclight@c9264c8