JWT encoding/decoding improvements

[micahmo]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• 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:

• Did you follow the code style guideline as described in CONTRIBUTING.md
• 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
• Did you verify that all unit tests pass
• If necessary and if possible, did you verify your changes on:
  • 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? :)

[btiteux]

Hello, sorry for the late review lot's of stuff in my personal life.

Everything is good for me for this new pull request.

[veler]

Thank you so much again for this pull request :D !