updated the lambda permission with the correct case

[tomellis91]

Issue #, if available:
The default policy action that get's added to the function permissions is in the incorrect case. It is being inserted as lambda:invokeFunction instead of lambda:InvokeFunction (note the i).
This means the permissions don't work as expected.

The correct case can be seen in the documentation here:
https://docs.aws.amazon.com/lambda/latest/dg/lambda-api-permissions-ref.html

When triggering the function via API gateway as a GET request the response returns as:

Unable to determine service/operation name to be authorized

This occurred when creating a CFN resource with Type: AWS::Serverless::Function

Description of changes:
I have updated the lambda action so that it is in the correct case: lambda:InvokeFunction

When creating the lambda the default policy is being added as:
"Principal": {
"Service": "apigateway.amazonaws.com"
},
"Action": "lambda:invokeFunction",

I have not updated the tests as of yet as there are a large number of files with the lowercase character. If you are happy with the change, please add a comment and I can go and update the remaining files before the change is merged.

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

[tomellis91]

Hi @ShreyaGangishetty ,
I have updated the rest of the tests to include the correct case. There are a few conflicts that need to be resolved, however I don't have the ability to update them myself.

Is there anything else that you need from my end? I will be happy to help where possible.

Cheers,
Tom

[ShreyaGangishetty]

@tde908 I will check and resolve these merge conflicts. Thank you for submitting this PR

[codecov-io]

Codecov Report

Merging #1319 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           develop    #1319   +/-   ##
========================================
  Coverage    94.48%   94.48%           
========================================
  Files           78       78           
  Lines         4388     4388           
  Branches       871      871           
========================================
  Hits          4146     4146           
  Misses         116      116           
  Partials       126      126

Impacted Files	Coverage Δ
samtranslator/model/eventsources/push.py	90.53% <100%> (ø)	⬆️
samtranslator/model/api/api_generator.py	95.13% <100%> (ø)	⬆️

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[ShreyaGangishetty]

@tde908 I have resolved the merge conflicts and rebased. This PR looks good to me.