feat: Alias level critical as fatal

[bruno-garcia]

Following getsentry/sentry-docs#835

[codecov-io]

Codecov Report

Merging #182 into master will decrease coverage by <.01%.
The diff coverage is 66.66%.

@@ Coverage Diff @@## master #182 +/- ##
==========================================
- Coverage 64.65% 64.65% -0.01% 
==========================================
Files 83 83 Lines 8994 8996 +2 ==========================================
+ Hits 5815 5816 +1 - Misses 3179 3180 +1

Impacted Files	Coverage Δ
general/src/protocol/types.rs	74.6% <66.66%> (-0.16%)	⬇️

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