CDK version of existing pattern - multi-account-private-apigw

[j-liburd]

Description of changes:

Initial commit. This main takeaway of the pattern already exists as a SAM template. This pull request is for a CDK version of the pattern. Some components are different.

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[j-liburd]

I take back my comment of this PR being the CDK version of an existing pattern. That is not an accurate statement. The existing pattern shows how to invoke a Central Private API that has other Private APIs as targets. My pattern shows how to invoke a Central Regional REST API that has other Private APIs as targets.

[biswanathmukherjee]

Hi @j-liburd, can you please elaborate what is the difference between this PR and #2588

[biswanathmukherjee]

@j-liburd This needs to be submitted as an application rather than pattern considering the volume of code changes involved. Hence I am closing the PR. We are now accepting patterns with service to service connectivity with small amount of custom codes. However, you can submit this as an application.