Improve error message for an invalid ResourcePolicy element

[marekaiv]

Issue #, if available: n/a

Description of changes: Improve failure mode and error message when an invalid ResourcePolicy is specified.

Description of how you validated changes: unit tests

Checklist:

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

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 #2271 (baa9d24) into develop (e7a1496) will increase coverage by 0.92%.
The diff coverage is 97.12%.

@@             Coverage Diff             @@
##           develop    #2271      +/-   ##
===========================================
+ Coverage    93.58%   94.50%   +0.92%     
===========================================
  Files           90       95       +5     
  Lines         6124     6611     +487     
  Branches      1260     1333      +73     
===========================================
+ Hits          5731     6248     +517     
+ Misses         183      169      -14     
+ Partials       210      194      -16     

Impacted Files	Coverage Δ
samtranslator/model/lambda_.py	93.10% <ø> (ø)
samtranslator/model/api/http_api_generator.py	91.21% <75.00%> (+0.02%)	⬆️
samtranslator/model/api/api_generator.py	93.25% <75.60%> (-1.12%)	⬇️
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%)	⬆️
samtranslator/metrics/method_decorator.py	100.00% <100.00%> (ø)
samtranslator/metrics/metrics.py	100.00% <100.00%> (ø)
samtranslator/model/__init__.py	97.64% <100.00%> (ø)
... and 34 more

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