Include dependabot configuration file

[glatterf42]

This PR introduces a dependabot configuration file with the aim of automatically setting @khaeru and myself as assignees and reviewers for dependabot PRs.

How to review

I'm not entirely sure how to best test this config file. Can we point dependabot to this branch and wait for the next PR to pop up? Apart from that, you can check that the file is following the official guidelines. It pieces together a few options, namely assignees, labels, and reviewers. The package-ecosystem is the same for pip and poetry and there is a note for pip and pip-compile.

• Read the diff and note that the CI checks all pass.

PR checklist

• [x] Continuous integration checks all ✅
• ~[ ] Add or expand tests; coverage checks both ✅~ No new functionality.
• ~[ ] Add, expand, or update documentation.~ Nothing user facing added.
• ~[ ] Update release notes.~ Nothing user facing added.

[codecov[bot]]

Codecov Report

Merging #748 (87e0553) into main (248bcbd) will not change coverage. The diff coverage is n/a.

@@          Coverage Diff          @@
##            main    #748   +/-   ##
=====================================
  Coverage   94.3%   94.3%           
=====================================
  Files         43      43           
  Lines       3474    3474           
=====================================
  Hits        3279    3279           
  Misses       195     195