JWT encoding/decoding improvements

[micahmo]

Pull request type

Please check the type of change your PR introduces:

• [x] Bugfix
• [x] New feature or enhancement
• [ ] UI change (please include screenshot!)
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes
• [ ] Internationalization and localization
• [ ] Other (please describe):

What is the current behavior?

Issue Number: N/A

What is the new behavior?

This PR includes a few improvements to JWT encoding/decoding.

• Allow encoding tokens with RSA private keys
• Make the header field readonly in encoding mode (since it doesn't currently affect the output, although that could be a future enhancement)
• Allow validating signature with a certificate containing a public key
• Fix an issue where the saved token algorithm was not loaded correctly

Other information

Quality check

Before creating this PR:

• [x] Did you follow the code style guideline as described in CONTRIBUTING.md
• [x] Did you build the app and test your changes?
• [ ] Did you check for accessibility? On Windows, you can use Accessibility Insights for this.
• [ ] Did you verify that the change work in Release build configuration
• [x] Did you verify that all unit tests pass
• [ ] If necessary and if possible, did you verify your changes on:
  • [x] Windows
  • [ ] macOS (DevToys 2.0)
  • [ ] Linux (DevToys 2.0)

[veler]

@btiteux , as you own this tool and know better about JWT than I do, could you please take a look at this PR? :)