Add DocC publish workflow to automate GitHub pages content

[kublaios]

Currently, we have to run the following command locally and commit the generated docs directory under gh-pages branch:

swift package --allow-writing-to-directory docs \
    generate-documentation \
    --target CutwormBDD \
    --disable-indexing \
    --transform-for-static-hosting \
    --output-path docs

P.S. For this to work, https://github.com/apple/swift-docc-plugin needs to be in package dependencies.

We can automate this step as described here: https://danielsaidi.com/blog/2024/03/10/automating-docc-for-a-swift-package-with-github-actions