Replace Managed Policy with equivalent inline policy

[ConnorKirk]

Some scanners are triggered by the presence of the AmazonAPIGatewayInvokeFullAccessmanaged policy. This commit replaces the managed policy with an equivalent inline policy that will not trigger scanners. There's a small security win in being able to scope the API Gateway resource to the specific Account and Region.

Issue #, if available:

Description of changes:

PR Checklist:

• [x] Changelog updated
• [x] Unit tests (and integration tests if applicable) provided
• [x] All tests pass
• [x] Pre-commit checks pass
• [x] Debugging code removed
• [x] If releasing a new version, have you bumped the version in the main CFN template?

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

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.71%. Comparing base (cb48fca) to head (2c596e2).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #405 +/- ## ======================================= Coverage 99.71% 99.71% ======================================= Files 31 31 Lines 1742 1742 ======================================= Hits 1737 1737 Misses 5 5 ```

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