feat(docker): build and publish unprivileged Docker image

[sgaist]

Description

This PR:

• adds a new Dockerfile that will build from the nginx unprivileged image
• modify the pipeline so that it builds images for both standard and unprivileged images

Similar to swagger-api/swagger-editor#3705

Motivation and Context

This will allow to deploy Swagger-UI on clusters such as OpenShift without having to meddle with the security context and security context constraints.

Fixes #10254

How Has This Been Tested?

• Manual build of the Dockerfile.unprivileged image is successful
• Starting a container using this image is successful
• Starting a container using this image with a different user is successful
• No error logged during the startup

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• [] Dependency changes (any modification to dependencies in package.json)
• [] Bug fixes (non-breaking change which fixes an issue)
• [] Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.