feat: add oauth2 redirect route

[fMeow]

Description

Add oauth2 redirect handler route. The oauth2-redirect.html file is copied from master branch, with a little addition that accepts both snake case and camel cases flow name from oauth2 servers.

With this commit, swagger editor next can finally work with openId/oauth2 authorization_code workflow.

Motivation and Context

The swagger editor just don't handle oauth2/openIdConnect callback when using authorization_code workflow. It just complains that 404 not found.

The same configuration works in the https://editor.swagger.io/, which follows the master branch.

How Has This Been Tested?

I have manually test it in local development npm run start and npm run build. I think it can work in docker too.

Screenshots (if appropriate):

With this commit, the openid authorization workflow is finally working.

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.