Handle when function http event auth is not a string

[aahung]

Issue #, if available:

Description of changes:

Description of how you validated changes:

Checklist:

• Add/update tests using:
  • Correct values
  • Bad/wrong values (None, empty, wrong type, length, etc.)
  • Intrinsic Functions
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected

Examples?

Please reach out in the comments, if you want to add an example. Examples will be
added to sam init through https://github.com/awslabs/aws-sam-cli-app-templates/

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

[codecov-commenter]

Codecov Report

Merging #2234 (75417b2) into develop (e7a1496) will increase coverage by 0.96%.
The diff coverage is 98.42%.

@@             Coverage Diff             @@
##           develop    #2234      +/-   ##
===========================================
+ Coverage    93.58%   94.54%   +0.96%     
===========================================
  Files           90       95       +5     
  Lines         6124     6568     +444     
  Branches      1260     1323      +63     
===========================================
+ Hits          5731     6210     +479     
+ Misses         183      166      -17     
+ Partials       210      192      -18     

Impacted Files	Coverage Δ
samtranslator/model/lambda_.py	93.10% <ø> (ø)
samtranslator/plugins/globals/globals.py	99.05% <ø> (ø)
samtranslator/translator/logical_id_generator.py	100.00% <ø> (+9.09%)	⬆️
samtranslator/region_configuration.py	77.77% <63.63%> (-22.23%)	⬇️
samtranslator/swagger/swagger.py	94.02% <94.23%> (+0.66%)	⬆️
samtranslator/model/api/api_generator.py	94.69% <96.55%> (+0.33%)	⬆️
samtranslator/__init__.py	100.00% <100.00%> (ø)
samtranslator/feature_toggle/dialup.py	100.00% <100.00%> (ø)
samtranslator/feature_toggle/feature_toggle.py	100.00% <100.00%> (+12.16%)	⬆️
samtranslator/intrinsics/actions.py	98.75% <100.00%> (+0.03%)	⬆️
... and 36 more

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[marekaiv]

method_authorizer might have been updated in the preceding if ... do we know that DefaultAuthorizer is a string (was that previously checked?). If not, we could consider turning this into an if rather than elif.

[aahung]

Good call, DefaultAuthorizer being a dict should not produce this error message (instead, it has its own message). Fixed. I also added an extra unit test to ensure only DefaultAuthorizer related error message is generated when it happens.