Prerender cdk v2 hotfixes

[AdamJHall]

Description of the proposed changes
This PR fixes a couple of issues:

1. Unable to passthrough required props to Lambda functions when using the PrerenderLambda construct
2. Esbuild fails for lambda functions due to not being wrapped in json.stringify
3. Cannot use a real VPC object when passing to the PrerenderFargate construct as all references to the vpcId MUST be a string and cannot be a ref

Notes to PR author

⚠️ Please make sure the changes adhere to the guidelines mentioned here

Notes to reviewers

🛈 When you've finished leaving feedback, please add a final comment to the PR tagging the author, letting them know that you have finished leaving feedback

[TheOrangePuff]

LGTM