Typo in Properties for Api in template is not handled with 4xx error

[ylynn]

Description:
Template with a typo in template is not handled as expected. Under Properties of an api event, use "methid" instead of "method". Get 5xx error.

Steps to reproduce the issue:

1. Create an template with an Api event, under "Properties", use "methid" instead of "method"
2. Publish to aws serverless application repository

Observed result:
Get a 5xx error

Expected result:
Should be handled as a 4xx with error message

[jlhood]

Was able to reproduce this issue. Transform error when Method isn't present due to misspelling:

Traceback (most recent call last):
  File "./sam-translate.py", line 65, in <module>
    main()
  File "./sam-translate.py", line 49, in main
    sam_template, {}, ManagedPolicyLoader(iam_client))
  File "/Users/keeton/workplace/GitHub/keetonian/serverless-application-model/samtranslator/translator/transform.py", line 16, in transform
    return translator.translate(input_fragment, parameter_values=parameter_values)
  File "/Users/keeton/workplace/GitHub/keetonian/serverless-application-model/samtranslator/translator/translator.py", line 55, in translate
    sam_plugins=sam_plugins
  File "/Users/keeton/workplace/GitHub/keetonian/serverless-application-model/samtranslator/parser/parser.py", line 12, in parse
    sam_plugins.act(LifeCycleEvents.before_transform_template, sam_template)
  File "/Users/keeton/workplace/GitHub/keetonian/serverless-application-model/samtranslator/plugins/__init__.py", line 136, in act
    raise ex
KeyError: 'Method'

The issue is that the implicit API plugin is assuming the Method property is there:

https://github.com/awslabs/serverless-application-model/blob/develop/samtranslator/plugins/api/implicit_api_plugin.py#L191

We need to patch implicit_api_plugin.py to be more defensive. Should use get() instead of assuming property keys are present.

[keetonian]

Released with SAM v1.11.0!