Add alert configurations

[stormsilver]

Purpose

Provide support for alert configurations (https://github.com/akshaykarle/terraform-provider-mongodbatlas/issues/7)

Notable changes

• Add CRUD support for alert configurations.
• There is some badness in the API where it will reject requests that specify "metricThreshold":{} when it doesn't want it. I had to override MarshalJSON and conditionally set that property. Please let me know if there's a better way to do this.
• Add support for outputting API requests/responses to a file to make it easier to debug the API interactions. I hope this isn't already achievable via some obvious environment variable - I'm new to Go and I couldn't find a way.

[akshaykarle]

Thanks for giving it a shot @stormsilver. Let me know once you hear from the Mongo Atlas people. Could you also look at the failing tests?

[codecov-io]

Codecov Report

Merging #4 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #4   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          10     11    +1     
  Lines         252    305   +53     
=====================================
+ Hits          252    305   +53

Impacted Files	Coverage Δ
mongodbatlas/mongodb.go	100% <100%> (ø)	:arrow_up:
mongodbatlas/alert_configurations.go	100% <100%> (ø)

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[stormsilver]

@akshaykarle Okay, I've addressed those failing tests. Sorry about that. I've heard back from the MongoDB Atlas support folks and they have acknowledged the bug on their side, but I don't think it will affect the code here (this code ought to just start working when they fix their bug).

I have blemished your otherwise perfect code coverage record. Since I'm not really familiar with Go, I'm not sure how to test the SlingLogger part which is really just for debugging purposes anyway. If you are able to provide me a little bit of direction I will take a stab at testing it; or if you have other thoughts (remove it, change it, etc) I'm certainly open to those as well.

I think this is ready to merge barring any changes regarding code coverage.

[stormsilver]

@akshaykarle this should be ready to merge now. The Atlas folks have released the fix for the bug and I have tested it and confirmed it works. Let me know if there is anything else for me to do here; otherwise as soon as this is merged I'll update my terraform plugin branch.

[akshaykarle]

Thanks @stormsilver. Can we just get rid of the DEBUG_SLING? I can then just merge it in.

[stormsilver]

@akshaykarle Done

[akshaykarle]

Thanks a lot @stormsilver :)