fix: catch error caused by improper event configuration

[keetonian]

Issue #, if available:
#766
Description of changes:
Handle key error from missing event keys.
Description of how you validated changes:

Checklist:

• Write/update tests
• make pr passes
• Update documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #845 into develop will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #845      +/-   ##
===========================================
+ Coverage    94.54%   94.55%   +<.01%     
===========================================
  Files           67       67              
  Lines         2824     2827       +3     
  Branches       508      508              
===========================================
+ Hits          2670     2673       +3     
  Misses          81       81              
  Partials        73       73

Impacted Files	Coverage Δ
samtranslator/plugins/api/implicit_api_plugin.py	96.35% <100%> (+0.08%)	⬆️

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