Update scheduled workflow to use pages v4

[Rylan12]

Closes Homebrew/brew#17379

This PR modifies the scheduled regeneration workflow to mimic the one used for formulae.brew.sh.

I've removed the generated site files from docs and updated the .gitignore file appropriately. If we want, we could rewrite the history of the repo to remove the generated files and make cloning take much less time (I can't remember whether we did that for formulae.brew.sh or not).

The scheduled task now has three jobs:

1. generate generates the site from Homebrew/brew, and also builds the site (i.e. runs bundle exec rake yard build). I figured because there is only one generation task, there's no real benefit to splitting this up into a separate generate and build job, but we can do that if we want to more closely mimic formulae.brew.sh
2. deploy deploys the site to GitHub pages
3. deploy-issue opens/closes deploy failure issues just like in formulae.brew.sh

[MikeMcQuaid]

Wow, great work here @Rylan12!

[MikeMcQuaid]

If we want, we could rewrite the history of the repo to remove the generated files and make cloning take much less time (I can't remember whether we did that for formulae.brew.sh or not).

We did for formulae.brew.sh and I just did for rubydoc.brew.sh, thanks!