Rename config files with .sample extension

[mark-dce]

Follow the usual convention of renaming config files saved in the repo so new deployments don't overwrite production configurations.

• [ ] rename yaml files
• [ ] add to .gitignore

[mark-dce]

Using solution from jcoyne instead - use git --assume-unchanged:

git update-index --assume-unchanged config/jetty.yml
git update-index --assume-unchanged config/application.yml