Add a `use_webr_github_pages()` to encourage developmental R WASM binaries

[coatless]

With webR picking up steam, it would be good to provide a top-level function that simplifies the way to incorporate development WASM binaries. Thus, I'm proposing the addition of a use_webr_github_pages()/use_rwasm_github_pages() function. There is a prior precedent for such a function based on integrating pkgdown with GitHub actions in the use_pkgdown_github_pages() function.

The inclusion of development WASM binaries requires the use of reproducible actions at r-wasm/actions to set up a CRAN-like repository and deploy it to the repository's GitHub Pages. So, the proposed function would likely using use_github_action() to obtain the deployment action and use_github_pages() to setup the gh-pages branch of the repository if it is not present already. Moreover, I'm not sure if further tweaks would be required to ensure the action plays nicely with a pkgdown website created using use_pkgdown().

I'm more than happy to investigate further and propose a working function if this is of interest.