Ensure all keyboards have a bootloader set

[fauxpark]

Description

As a result of #18228 removing the default bootloader assignment and adjusting the makefile logic to complain if no bootloader is set, or an invalid one for the given platform:

Failing builds:
  clueboard/17:default
  clueboard/66/rev1:default
  clueboard/66/rev1:via
  clueboard/66/rev2:default
  clueboard/66/rev2:via
  clueboard/66/rev3:default
  clueboard/66/rev3:via
  clueboard/66_hotswap/prototype:default
  clueboard/card:default
  handwired/3dortho14u/rev1:default
  handwired/3dortho14u/rev1:via
  handwired/3dortho14u/rev2:default
  handwired/3dortho14u/rev2:via
  handwired/dactyl_manuform/4x5_5:default
  handwired/dactyl_manuform/dmote/62key:default
  handwired/hillside/46:default
  handwired/hillside/46:via
  handwired/hillside/48:default
  handwired/hillside/48:via
  handwired/hillside/52:default
  handwired/hillside/52:via
  handwired/wakizashi40:default
  handwired/wakizashi40:via
  lfkeyboards/lfk65_hs:default

I was worried there'd be much more, honestly.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).