Enable automatic dependency updates for this repo

[cmeister2]

It'd probably be a good idea to keep this repo's dependencies up to date.

• I don't think dependabot will work because the files are not in a supported format: https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#package-ecosystem
• https://github.com/renovatebot/renovate will probably work as it supports Github Tags (amongst lots of other dependency types) but it will require onboarding and configuring.

[cmeister2]

Renovate is up and running and seems to be doing good stuff.