feat(Theming): Adds theming support with documentation.

[markrickert]

Please verify the following:

• [x] yarn test jest tests pass with new tests, if relevant
• [x] yarn lint eslint checks pass with new code, if relevant
• [x] yarn format:check prettier checks pass with new code, if relevant
• [x] README.md (or relevant documentation) has been updated with your changes

Describe your PR

This PR adds theming support to the ignite boilerplate as well as relevant documentation on how to use the theming system.

Note that this PR is onto the v10 branch and not main.

[jamonholmgren]

Before we merge this, I want to make sure we get some real-world experience. @markrickert you're starting a new project soon, so this will be a good opportunity for that.

[markrickert]

@jamonholmgren Absolutely. I'll keep this branch up to date with main and use this as the starting point for my next project.

[markrickert]

Rebased on the v10 branch and fixed a few issues caused by the Switch/Toggle rewrite