Github Actions: Add action that checks for dependency issues

[axe312ger]

While developing, you can accidentally use dependencies from other packages. This works fine on your machine, but as soon your publish this, it might cause issus in other people projects

For this we already have the npm run check-dependencies script in the root package.

• create a action that executes that script
• exclude starters + theme or go crazy and add gatsby support to depcheck