Allow Lambda Aliases To Be Used With Constructs

In a [Re:Invent video about CDK Pipelines](https://youtu.be/1ps0Wh19MHQ?t=2339), they demoed using lambda aliases to perform canary and linear rollouts of lambdas to a stack. However it does not appear that any of the official CDK Constructs Solutions (let alone the community ones) allow for using a lambda alias as the existing lambda reference.

### Use Case

Allow canary and linear rollout of lambda changes in conjunction with integration tests on deployment when using CDK Solutions Constructs with CDK Pipelines.

### Proposed Solution

```js
{
existingLambda: /* IFunction instead of Function */
}
```

### Other

* [ ] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

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This is a :rocket: Feature Request