feat(alerting): Add Pushover provider

[Kovah]

Summary

I am not sure if I missed something. There are a lot of files where providers are referenced, but I think I got all of them.

• Adds new provider named Pushover with corresponding tests
• Adds Pushover as a provider to the configuration and adjusts test accordingly
• Adds Pushover to alerting_test.go, provider.go and type.go
• Updates the readme with configuration details

Before merging: what would be the best way to properly test this with real API calls? Is there any process defined or should I just try to build it and check if a config works?

Additional thoughts/ideas that could be implemented later:

• Add support for other configuration options, like device support, the Gatus URL in it or setting a sound
• Allow overriding of title, priority,... per group like the PagerDuty provider does.
• Allow usage of placeholders in title and description like the custom provider does.

Related: ##129

Checklist

• Tested and/or added tests to validate that the changes work as intended, if applicable.
• Added the documentation in README.md, if applicable.

[codecov-commenter]

Codecov Report

Base: 82.00% // Head: 81.98% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (b99d14d) compared to base (90bb8f7).
Patch coverage: 86.66% of modified lines in pull request are covered.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #405      +/-   ##
==========================================
- Coverage   82.00%   81.98%   -0.02%     
==========================================
  Files          55       56       +1     
  Lines        4178     4225      +47     
==========================================
+ Hits         3426     3464      +38     
- Misses        586      592       +6     
- Partials      166      169       +3     

Impacted Files	Coverage Δ
alerting/provider/provider.go	100.00% <ø> (ø)
alerting/provider/pushover/pushover.go	86.36% <86.36%> (ø)
config/config.go	76.06% <100.00%> (+0.10%)	⬆️
config/maintenance/maintenance.go	96.20% <0.00%> (-3.80%)	⬇️
controller/handler/handler.go	79.41% <0.00%> (+1.28%)	⬆️

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[Kovah]

I have built the Docker container with the latest changes and tested it with this config:

---
debug: true

alerting:
  pushover:
    application-token: ar5k...wkg4
    user-key: 2ZHm...cWed
    title: "Pushover Gatus Test"
    default-alert:
      enabled: true
      description: "Healthcheck failed for [ENDPOINT_URL]"
      failure-threshold: 1
      success-threshold: 1
      send-on-resolved: true

endpoints:
  - name: dashboard
    url: https://my-private-domain.com
    interval: 30s
    alerts:
      - type: pushover
    conditions:
      - "[STATUS] == 200"

Working as expected.

What I would like to add before merging this is to add support for placeholders in title and description like the custom provider does. I think this should be handled by a helper function so that there's no code duplication, because currently it's just hardcoded into the custom provider. Any thoughts an that?

[TwiN]

@Kovah Support for placeholders will be handled separately.

See #287

[TwiN]

Before merging: what would be the best way to properly test this with real API calls? Is there any process defined or should I just try to build it and check if a config works?

Using the MockRoundTripper just like in PagerDuty was the right approach, and you've already done it.

There's a couple of integration tests that send real requests, but I try to avoid them as much as possible, and when it's unavoidable, I either use a website that I own or a stable public service (e.g. example.com, example.org, a public DNS, etc.), because they have predictable outputs or I can control the outputs myself.

As such, I wouldn't feel really comfortable having an integration test for something like pushover unless they explicitly provide permission.

[TwiN]

@Kovah Excellent work!
Thank you for the contribution!

[Kovah]

Great, thanks for merging!