Implement mailcow widget

[grimsi]

Proposed change

Note: This is a DRAFT PR subject to the 10 upvote requirement. As soon as this requirement is fulfilled I will convert this into a normal PR so it can be merged if it passes all checks.

Implement a widget for Mailcow.

Closes #3548

Preview:

Type of change

• [x] New service widget
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Documentation only
• [ ] Other (please explain)

Checklist:

• [x] If applicable, I have added corresponding documentation changes.
• [x] If applicable, I have reviewed the feature and / or service widget guidelines.
• [x] I have checked that all code style checks pass using pre-commit hooks and linting checks.
• [x] If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.

[shamoon]

Please reopen at the appropriate time

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