chore: add dependabot config

[siljekristensen]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Add a dependabot config

• What is the current behavior? (You can also link to an open issue here)

• What is the new behavior (if this is a feature change)?

• Other information:

[codecov-commenter]

Codecov Report

Base: 85.98% // Head: 85.98% // No change to project coverage :thumbsup:

Coverage data is based on head (6226dec) compared to base (da0d841). Patch has no changes to coverable lines.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #137 +/- ## ======================================= Coverage 85.98% 85.98% ======================================= Files 166 166 Lines 5339 5339 Branches 892 892 ======================================= Hits 4591 4591 Misses 728 728 Partials 20 20 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nrkno). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nrkno)

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