fix(elbv2): unable to specify load balancer name

[eladb]

Since #973, the renames of CFN properties from "name" to "xxxName" were
removed. But the ELBv2 library still used loadBalancerName. The reason
this was not discovered was because we are splatting additionalProps of
type any, and this caused the type checker to stop verifying property
names.

Fixes #1481

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Pull Request Checklist

• Testing
  • Unit test added
  • CLI change?: manually run integration tests and paste output as a PR comment
  • cdk-init template change?: coordinated update of integration tests with team
• Docs
  • jsdocs: All public APIs documented
  • README: README and/or documentation topic updated
• Title and Description
  • Change type: title prefixed with fix, feat will appear in changelog
  • Title: use lower-case and doesn't end with a period
  • Breaking?: last paragraph: "BREAKING CHANGE: <describe what changed + link for details>"
  • Issues: Indicate issues fixed via: "Fixes #xxx" or "Closes #xxx"
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  • IAM Policy Document (in @aws-cdk/aws-iam)
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[mergify]

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• PR title type(scope): text
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