chore: add e2e cdk lambda fixture

[ava-silver]

What does this PR do?

Second of a 3-PR stack (#625 → #626 → #627). Adds the CDK app the e2e suite drives (e2e/app/): a single Lambda workload plus its handler.

The same WorkloadStack serves both phases via E2E_INSTRUMENT:

• false -- a bare lambda.Function, the uninstrumented baseline.
• true -- the function wrapped by the DatadogLambda construct (pinned Node + extension layers, tracing/logs, run-id tag).

Motivation

The construct is the instrumentation mechanism under test, so the fixture imports DatadogLambda from src/ directly -- the suite exercises this repo's construct code, not a published package. Landing the deployable on its own keeps it reviewable in isolation; the test that drives it lands in #627.

Testing Guidelines

No standalone run -- the app is synthesized and deployed by the test suite at the top of the stack (#627).

Additional Notes

A freshness tag is set at creation on the baseline too, so the cross-repo sweeper can reap the function if a run crashes before teardown.

Types of Changes

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

Check all that apply

• 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

[ava-silver]

• chore: add e2e lambda lifecycle test and workflow #627
• chore: add e2e cdk lambda fixture #626 👈 (View in Graphite)
• chore: add synced e2e shared helpers #625
• main

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