Add check-in configuration sync

[stympy]

trafficstars

We'd like people to be able to configure their check-ins via the gem/API, rather than having to use the app UI. This would allow for new cron jobs, etc., to be deployed and have the monitoring set up automatically.

This implementation should be similar to the Laravel implementation.

[halfbyte]

I'll have a go at this, should give me some good insights into API interaction etc.

[subzero10]

@halfbyte I've only recently completed the PHP/Laravel implementation and I'm currently on the JS implementation. So, feel free to reach out for requirements/questions/feedback. Here's the documentation page for the guide on PHP/Laravel.