Refac generated documentation (!254)

* revert gen-doc changes

* Revert "add doc to CI"

This reverts commit 7f086905.

* update xtask to polkadot-v1.9.0

* add doc to CI

* reduce doc size

* move runtime api doc to target artefact

* add base url

* enable full docs for non-local pallet

* add url to rust autogenerated docs in api

* add rust doc generation

* remove gen-doc file from git index

* fix xtask gen-docs