Add Miniflux Service

[reikkaps]

Description

This service displays a version string instead of a subtitle. The indicator
shows if Miniflux is online or offline. Miniflux is a minimalist and opinionated feed reader:

https://miniflux.app/

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• [x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I've read & comply with the contributing guidelines
• I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• I have made corresponding changes to the documentation (README.md).
• [ x] I've checked my modifications for any breaking changes, especially in the config.yml file