Add base64-url content encoding

[bschoenmaeckers]

Description

I added the commonly used base64url content encoding.

After this addition swagger should be able to generate example data for the following schema:

{
  "type": "string",
  "contentMediaType": "application/json",
  "contentEncoding": "base64url",
  "contentSchema": {
    "$ref": "#/components/schemas/Pet"
  }
}

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

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.

[char0n]

Hi @bschoenmaeckers,

base64url is mentioned explicitly in https://www.rfc-editor.org/rfc/rfc4648.txt which means it can added to core encodings SwaggerUI supports - basically in the exact way as you did in your PR.

Thank you for contributing!

[char0n]

LGTM