Add Gherkin Support

[ericmcbride]

Added Gherkin (Feature File) support. We currently use prettier-plugin-gherkin for linting our feature files, and we use the aspect_rules_lint for everything else. Wanted to add this feature so we don't have to maintain a one off.

Changes are visible to end-users: yes/no

Adds a new feature for users to use prettier-plugin-gherkin w prettier to add functionality to formatting feature files.

Test plan

• Covered by existing test cases
• Added an example

[CLAassistant]

All committers have signed the CLA.

[ericmcbride]

@alexeagle

[alexeagle]

Thanks!

[ericmcbride]

@alexeagle I made the changes. Im running the 2 tests that failed locally and im running the suggestions but they are not working. I didnt touch the files so im confused whats going on there

[alexeagle]

@ericmcbride yeah the suggested fix command is incorrect, as pointed out in #482

I'll get this green and landed :)