feat(langfuse): langfuse tracing sample app

[athewsey]

Issue #, if available: https://github.com/awslabs/generative-ai-cdk-constructs/issues/1031

Description of changes:

Add a new deployable sample app companion for https://github.com/awslabs/generative-ai-cdk-constructs/pull/1037 - showing how to use the constructs to deploy a self-hosted Langfuse environment, and then instrument Lambda function(s) to send traces into Langfuse when calling Bedrock.

Marking ready for review as this is now tested working end-to-end, but with outstanding actions:

• [ ] Update package.json to sensible versions of aws-cdk-lib, constructs, @aws-cdk/aws-lambda-python-alpha, and @cdklabs/generative-ai-cdk-constructs when the constructs library is released

Feedback very welcome!

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[athewsey]

I'm actually having some trouble with the "file://../../../generative-ai-cdk-constructs" dependency in package.json ending up with a load of typing errors because it seems to result in multiple parallel versions of aws-cdk-lib and etc... Any tips on avoiding this?

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Update: Seems to be working as of b1fd0f5d4b24c57a0b28b8adf0f763442c5e1d1c (using npm link to link in the local construct library package), but I'm still working through issues with CDK-Nag