Editorconfig checker

[yubiuser]

• What does this PR aim to accomplish?:

Adds an editorconfig-checker (https://github.com/editorconfig-checker/editorconfig-checker) GH action (https://github.com/editorconfig-checker/action-editorconfig-checker).

It also adds the configuration for yml files to editorconfig.

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1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

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