Add Dependabot configuration

[Nardol]

Add Dependabot for GitHub action, Gradle and Swift.

[bear101]

Do you have an example where this comes into play?

[Nardol]

Not the same package ecosystems except for GH actions, but here you can find some example of Dependabot pull requests.

There is also a demo repository to fork and see Dependabot in action.

[Nardol]

Do you have an example where this comes into play?

For example, you won't have to update GitHub actions manually anymore, as soon as a new version is available, Dependabot will automatically open a pull request to update the version in every workflows which use the outdated version.

[bear101]

We'll update the dependencies manually. Then we're more in control if things break.