Stop depending on Linter

[konn]

First of all, thank you for creating this extension!

By the way, the dependent Linter extension makes other LSPs too slow and there is some issue around it:

fnando/vscode-linter#41

It seems that the maintainer of Liter seems busy and this issue seems unlikely to be resolved anytime soon.
This bug prevents me from using actionlint with e.g. large Rust codebase - this is rather disappointing as it forces me to disable actionlint to edit seemingly unrelated language. Perhaps it would be good to drop the dependency to Linter and provide the custom dedicated linting mechanism.