hadolint for linting

[madhukar93]

https://github.com/hadolint/hadolint

A smarter Dockerfile linter that helps you build best practice Docker images. The linter is parsing the Dockerfile into an AST and performs rules on top of the AST. It is standing on the shoulders of ShellCheck to lint the Bash code inside RUN instructions.

This should make a good addition to the plugin. Thoughts?

[meinzer1899]

You can configure hadolint by using this configuration https://github.com/iamcco/diagnostic-languageserver/wiki/Linters#hadolint and map the filetype with
"diagnostic-languageserver.filetypes": { "dockerfile": "hadolint" } .

Alternatively, you can use coc-diagnostic and just map the filetype.