fix: invalid event type error

[praneetap]

Issue #, if available:
#915
Description of changes:
handle Attribute error in sam_resources to return a 4xx error for invalid event type in function
Description of how you validated changes:
Added tests for bad event type and ran make pr.
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 #918 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           develop     #918   +/-   ##
========================================
  Coverage    94.66%   94.66%           
========================================
  Files           69       69           
  Lines         3016     3016           
  Branches       561      561           
========================================
  Hits          2855     2855           
  Misses          85       85           
  Partials        76       76

Impacted Files	Coverage Δ
samtranslator/model/sam_resources.py	95.5% <100%> (ø)	⬆️

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