* Refactor remote_externalities::rpc_api

* try-runtime-cli: Adde `execute-block` subcommand

* Trivial

* Address some comments

* Use required_if & remove header-at usage

* Improve doc

* Update comment

* small tweaks

* add overwrite-code to shared params

* Update utils/frame/try-runtime/cli/src/lib.rs

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* make url a shared param

* add helper for block_at (#9153)

* add helper for block_at

* remove redundant bound

* doc for fn block_at

* Update error message

Co-authored-by: kianenigma <kian@parity.io>
Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>