Events API Authorization (Event Type Authorizer)

[mthenw]

What did you implement:

Authorizer for event type

How did you implement it:

TODO

Todos:

• remove space from metricEventsDropped metric
• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: NO
Is it a breaking change?: YES

[codecov]

Codecov Report

Merging #441 into master will decrease coverage by 0.63%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##           master     #441      +/-   ##
==========================================
- Coverage   65.38%   64.74%   -0.64%     
==========================================
  Files          32       32              
  Lines        1788     1835      +47     
==========================================
+ Hits         1169     1188      +19     
- Misses        573      596      +23     
- Partials       46       51       +5

Impacted Files	Coverage Δ
router/wait.go	0% <0%> (ø)
internal/cache/target.go	0% <0%> (ø)	⬆️
router/metrics.go	35.29% <0%> (-17.65%)	⬇️
event/type.go	0% <0%> (ø)	⬆️
libkv/eventtype.go	87.87% <100%> (+0.78%)	⬆️
internal/cache/subscription_cache.go	86.76% <100%> (+0.61%)	⬆️
router/router.go	62.83% <61.71%> (+8.91%)	⬆️
... and 1 more

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