Add support to create config variables to avoid hard-coded strings

[priyamsahoo]

Supporting config variable is out of the scope as of now. It can be viewed as a separate task and I am going to look into it.

Originally posted by @priyamsahoo in #5 (comment)

[webknjaz]

It looks like this would need client-side support. It should probably send options as in this example: https://github.com/redhat-developer/vscode-java/blob/af081b9/src/standardLanguageClient.ts#L70-L92.

[webknjaz]

Our extensions sets those here: https://github.com/ansible/vscode-ansible/blob/5ef7df7/src/extension.ts#L29-L48.

[priyamsahoo]

Some of the config variables that we can use in language server are here in this file.