feat: make new url constructor in core package able to work with api

[bartoszherba]

Description

Currently, core package is throwing an error Invalid URL when middlewareUrl is set to "/api” .

We need to make it able to work with such a values.

Change is required to be done in packages/core/src/utils/nuxt/_proxyUtils.ts file and it should NOT be a breaking change.

New core version is necessary to be released.

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots:

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have read the CONTRIBUTING document.

Changelog

• [ ] I have updated the Changelog (V1) v2 and mentioned all breaking changes in the public API.
• [ ] I have documented all new public APIs and made changes to existing docs mentioning the parts I've changed so they're up to date.

Tests

• [x] I have written test cases for my code
• [ ] I have tested my Pull Request on production build and (to my knowledge) it works without any issues
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

  I tested manually my code, and it works well with both:

• [ ] Default Theme
• [ ] Capybara Theme

Code standards

• [x] My code follows the code style of this project.
• [ ] I have followed naming conventions

Docs

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.