[core] Providing an official string constants Service principal and Managed Policy, etc

Similar to this repo here: https://github.com/kevinslin/cdk-constants/blob/master/lib/services.ts
I would love to have an AWS officially maintained constant files with all the available Service Principal and Manged policy, service name, service endpoint, etc.

### Use Case
It makes development on CDK much faster without the need for me look up any IAM documents on the web and I could just simply import an value.

Also, having an official list of constants gives me the comfort that I don't need to worry about that the list contains outdated or unsupported strings.

### Proposed Solution

Should be a simple TS file exporting all the constants.
Would need some AWS internal validations that those are correct.

### Other

* :wave: I may be able to implement this feature request

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This is a :rocket: Feature Request

Start by reviewing the referenced lib/services.ts example and the AWS CDK TypeScript structure. The issue does not name a target file or tests, so first clarify which constant categories and validation sources are in scope. Done would require an agreed set of officially maintained constants with AWS validation.

Written by the indexing model from the issue text.