alerting: added slack as a notifier

[darwinz]

Fixes: #52

[codecov-commenter]

Codecov Report

Merging #101 (59c0a57) into master (961efe1) will decrease coverage by 0.48%.
The diff coverage is 3.84%.

@@            Coverage Diff             @@
##           master     #101      +/-   ##
==========================================
- Coverage   42.08%   41.60%   -0.49%     
==========================================
  Files          87       88       +1     
  Lines        3647     3644       -3     
==========================================
- Hits         1535     1516      -19     
- Misses       1817     1841      +24     
+ Partials      295      287       -8     

Impacted Files	Coverage Δ
internal/alerting/alerter.go	0.00% <0.00%> (ø)
internal/alerting/pagerduty.go	0.00% <0.00%> (ø)
internal/alerting/slack.go	0.00% <0.00%> (ø)
internal/service/model_errors.go	13.33% <0.00%> (-4.85%)	⬇️
internal/incoming/odfi/scheduler.go	29.67% <40.00%> (-0.67%)	⬇️
internal/pipeline/aggregate.go	24.63% <66.66%> (-0.87%)	⬇️
internal/consul/leader.go	34.28% <0.00%> (-51.43%)	⬇️
internal/transform/gpg.go	48.38% <0.00%> (-18.28%)	⬇️
... and 8 more

---

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[adamdecaf]

Is there a use-case for warning alerters? We don't have a setup for determining when warnings occur, so I don't see them as being used now.

[darwinz]

Is there a use-case for warning alerters? We don't have a setup for determining when warnings occur, so I don't see them as being used now.

I can remove the warning alerters. I just thought it would be useful to give the option of having a non-critical notifier

[adamdecaf]

Is there a use-case for warning alerters? We don't have a setup for determining when warnings occur, so I don't see them as being used now.

I can remove the warning alerters. I just thought it would be useful to give the option of having a non-critical notifier

I can agree that's a useful feature, but the current code doens't handle it well.

[adamdecaf]

Awesome, thank you!