add redhat vscode-yaml lsp as dependency

[emilkje]

[emilkje]

@h3rmanj @JonasKs @daniwk This PR fixes #4 by adding redhat language server as a hard dependency. It would make the installation easier for the end user, but it would also take away the flexibility of choosing your own yaml lsp implementation. One could argue that redhat.vscode-yaml is the de-facto standard language server and would work perfectly fine >90% of the time, but in theory this could make intility.vscode-backstage unusable for some people.

I tried to find some mechanism to promote redhat.vscode-yaml as a recommended extension, but could only find extensionDependencies as an integration hook. I'm inclined to not merge this, but would appreciate some input in this regard.

[h3rmanj]

We should probably avoid adding it as a dependency unless we actually interact with it. One way we could do that, is set the correct scheme after a snippet has been used, so the user don't have to do it manually. The YAML extension will only set the correct scheme automatically if the file your editing is named catalog-info.yaml, but not for other files. Not sure if this is possible to achieve though.

For now I'm leaning towards just mentioning it in the readme, even though it would be a bit hidden.