feat(api-rest): allow relative URL's

[bobbor]

Description of changes

Improving the api URL resolution in case of relative URL's to include the locations origin
also fixing a false positive in the tests of the publicApi's

Issue #, if available

Amplify 6 - Cannot use a url relative url for the Rest API Endpoint url #13031

Description of how you validated changes

I have added tests to actually test the resolve URL. This includes tests for

• absolute URL's
• relative URL's
• url's without protocol

Checklist

• PR description included
• yarn test passes
• Unit Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

Checklist for repo maintainers

• Verify E2E tests for existing workflows are working as expected or add E2E tests for newly added workflows
• New source file paths included in this PR have been added to CODEOWNERS, if appropriate

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.