Update label automation to avoid docs linting changes
What does this MR do?
The labeling automation was adding documentation to some MRs where no docs were being changed, for example:
This adds regex to make sure it only adds the label for documentation changes, by searching on the extension: .md, .png, .jpg and .gif.
This way, if we change Vale rules (or possible future linters and config files) which are in .yml format, they won't cause this label automation to trigger.
Edited by Marcel Amirault