Bump bootstrap and admin-lte

Removes [bootstrap](https://github.com/twbs/bootstrap). It's no longer used after updating ancestor dependency [admin-lte](https://github.com/ColorlibHQ/AdminLTE). These dependencies need to be updated together.


Removes `bootstrap`

Updates `admin-lte` from 3.2.0 to 4.0.0-beta2
- [Release notes](https://github.com/ColorlibHQ/AdminLTE/releases)
- [Commits](ColorlibHQ/AdminLTE@v3.2.0...v4.0.0-beta2)

---
updated-dependencies:
- dependency-name: bootstrap
  dependency-type: indirect
- dependency-name: admin-lte
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>