feat(outcomes): Added support for client reported outcomes

[mitsuhiko]

This adds a new outcome type 5 which is reserved for recording events discarded on the client side.

Refs getsentry/relay#1074

[codecov-commenter]

Codecov Report

Merging #2081 (2e78965) into master (bfabb58) will increase coverage by 0.06%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #2081      +/-   ##
==========================================
+ Coverage   91.14%   91.21%   +0.06%     
==========================================
  Files         510      510              
  Lines       22191    22198       +7     
==========================================
+ Hits        20227    20247      +20     
+ Misses       1964     1951      -13     

Impacted Files	Coverage Δ
snuba/datasets/outcomes_processor.py	92.59% <75.00%> (-7.41%)	⬇️
snuba/cli/bootstrap.py	10.34% <0.00%> (+10.34%)	⬆️
snuba/cli/api.py	43.47% <0.00%> (+26.08%)	⬆️
snuba/cli/__init__.py	100.00% <0.00%> (+30.00%)	⬆️

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[fpacifici]

Some context on the volume we expect.
Do we have an idea of how many events are discarded by the sdk per second? Impact:

• we may need a bigger clickhouse cluster (it is possible but it takes time and needs some planning)
• The consumer is already spread fairly thin (8 replicas). We have work too do to make consumption of high volumes of small events more efficient.

[mitsuhiko]

@fpacifici i will do some estimates on this. I think we should try to merge this PR so that in case new outcomes come our way we gain the validation of the values.