website: Update to work within chisel3 repo.

- update README to have proper links to this version of the code
- Move website CI script to top level workflows, give some more unique names
- remove chisel3 submodule dependency from website
- website: Tweak to build within chisel3
- Add firtool as a dependency in CI and the README for the website
- website: remove dependabot file since we have no submodules
- add website to required CI checks

Update .github/workflows/test.yml

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>