fix: make DatadogProps available in Python again

[lym953]

What does this PR do?

Solves a few backward compatibility issues:

• Change DatadogProps from a type to an interface, so there will be a class DatadogProps in the generated Python package
• Create an interface DatadogStrictProps (which has been renamed to DatadogLambdaStrictProps in #288), in case it's still being used by any external code
• Create a const DefaultDatadogProps (which has been renamed to DatadogLambdaDefaultProps in #288), in case it's still being used by any external code

Motivation

Users reported that the class DatadogProps is no longer available in the Python package v2-1.16.0. https://github.com/DataDog/datadog-cdk-constructs/issues/294

Testing Guidelines

Steps

1. Make changes on the example Python stack to make it use DatadogProps https://github.com/DataDog/datadog-cdk-constructs/commit/480eed099a4836360e72365db6edcd1af1d43d36
2. Deploy the stack

   Result

   Before:

   • cdk deploy gives an error:

     ImportError: cannot import name 'DatadogProps' from 'datadog_cdk_constructs_v2'

After:

• cdk deploy runs successfully

Additional Notes

Types of Changes

• [x] Bug fix
• [ ] New feature
• [ ] Breaking change
• [ ] Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• [x] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [ ] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog

[lym953]

Since #288 is reverted, I'll rewrite the current PR and open another one.