feat: add theme switch on website home page

[shadab-taiko]

Fixes #13028

[RogerLamTd]

Looks good! Might want to make it a toggle button like the one on the bridge at the top of the page? Could make it easier to find and access.

[wolfderechter]

Looks good! Might want to make it a toggle button like the one on the bridge at the top of the page? Could make it easier to find and access.

I agree, it should be on top of the page, it's way too hard to find right now

[shadab-taiko]

Looks good! Might want to make it a toggle button like the one on the bridge at the top of the page? Could make it easier to find and access.

I agree, it should be on top of the page, it's way too hard to find right now
@RogerLamTd @wolfderechter
The Nextra theme that we are using places it like so and thus I have replicated it.

[Eleleth77]

agreed. Main page top right