[ci] Move build and publish rustdocs to GHA (#6047)

PR moves jobs `build-rustdoc`, `test-doc` and `publish-rustdoc` to GHA.
`publish-rustdoc` was changed so it can publish changes using token from
GH APP.
PR removes `test-rustdoc` because the same command in executed in
`build-rustdoc` and I see no reason to run it twice.

cc https://github.com/paritytech/ci_cd/issues/1006