long vignettes and tests

[topepo]

Some of the vignettes and tests take a really long time and rely on packages not in the description file.

I propose that:

• Move the vignettes to a sub-directory in vignettes
• Update the _pkgdown.yml so that these get build by GHA when the pkgdown site is updated.
• Temporarily park the tests using rsample and tune in a branch.
• Once we get closer to a release, move those tests to the extratests package (where we do cross-package system tests).

For the vignettes, they wouldn't be listed on the CRAN page but are shown on the pkgdown site. We could get them on the CRAN page if we made a page with a simple redirect. We do this for some longer running vignettes (like in workflowsets).