Auto merge of #17735 - alibektas:ratoml_workspaces, r=Veykril

feat: Introduce workspace `rust-analyzer.toml`s

In order to globally configure a project it was, prior to this PR, possible to have a `ratoml` at the root path of a project. This is not the case anymore. Instead we now let ratoml files that are placed at the root of any workspace have a new scope called `workspace`. Although there is not a difference between a `workspace` scope and and a `global` scope, future PRs will change that.

Author: bors