Update CSS Overrides and references to PF tokens in RHOAI + PF6 WIP PR

[nicolethoen]

take @jeff-phillips-18 WIP PR and run with it. Any questions on where to look for overrides, Jeff can help point people in the right directions.

PRs could be opened again the WIP PR, or commits can be made directly into the PR, depending on level of comfort.

Once we've made significant progress on these updates, we will engage with UXD designers (likely Jenn Giardino and Simran Dhaliwal) to do a design review of the PR, to check that nothing is broken or poorly formatted following the migration.

[thatblindgeye]

In AboutDialog, the styling of the Alert title looks off. Because it's rendered inside a Content component, there's margin-block-start styling being applied to the h4.pf-v6-c-alert__title element which pushes it down compared to the icon:

[thatblindgeye]

The custom Switch styling in frontend/src/app/App.scss needs to be updated, it's causing the Switch toggle to be misaligned due to the sizing update: