Migrate dependency updater to Dependabot

[mpeyper]

Describe the feature you'd like:

I've been using Renovate since before Dependabot was part of GitHub, but I think as this project is more popular than my others and more likely to have other contributors and maintainers involved, it's better to go with the more standard solution in this space.

I've got no experience with Dependabot though so any tips, tricks and pointers are much appreciated.

Suggested implementation:

Read the docs, add the config.

Describe alternatives you've considered:

N/A

Teachability, Documentation, Adoption, Migration Strategy:

N/A