feat: Expose an API for external applications to push statuses

[nioupola]

Describe the feature request

A API write option to perform adding (first), modify and delete endpoints from curl or requests library.

Why do you personally want this feature to be implemented?

I'm working to integrate gatus in my already setup integration tool you perform automatic configuration (like DNS or folder setup). It should be nice if we can add a new endpoint through the API to avoid modify manually the configuration file.

How long have you been using this project?

almost 6 months

Additional information

No response

[TwiN]

This is a duplicate of #95, but considering this PR uses the new issue template, I'm going to close #95 in favor of this.

[gp-Airee]

It really seems like these two issues are asking for something different. One wants to be able to modify the list of endpoints, one wants to do outbound health checks.

[hypervtechnics]

I also need this heartbeat behaviour. Maybe we can orient at the behaviour in uptime kuma?

[ser]

It would be fantastic to have outbound health check, replacing functionality of nagios or (super-heavy-on-resources-because-of-bad-programming-and-technology-choices) uptime-kuma.

[TwiN]

What I'd want to see for this would be:

1. The ability to configure a token for the admin API:

admin:
  token: "some-token"

2. An API (e.g. /api/v1/admin/endpoints/statuses) that can be used to create (POST) a new endpoint status using one of the aforementioned token through the Authorization: Bearer <token> header
3. The ability to mark an endpoint as "self-managed" to prevent the auto-clean system

   gatus/storage/store/store.go

   Lines 39 to 42 in f6a621d

   	// DeleteAllEndpointStatusesNotInKeys removes all EndpointStatus that are not within the keys provided
   	//
   	// Used to delete endpoints that have been persisted but are no longer part of the configured endpoints
   	DeleteAllEndpointStatusesNotInKeys(keys []string) int

   from wiping endpoint statuses that are directly monitored by Gatus. Something like:

endpoints:
  - name: "example"
    self-managed:
      enabled: true

(we need self-managed to be a struct/object here to future-proof this. I know we could just make it self-managed: true, but in the future, we might want to add certain behaviors unique to self-managed endpoints)

I'm open to other suggestions, but this is how I'd probably go about implementing this at the moment.

[truxnell]

I'm pretty keen on this one too. The ability to have a few applications call an uptime-kuma heartbeat check is the only thing stopping me from replacing UK with gatus!