feat: add discord driver

[Mesteery]

Proposed changes

Add the Discord OAuth2 driver.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have read the CONTRIBUTING doc
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[thetutlage]

Appreciate you taking out time to add proper types as well. Going to give it a test run in a while :)

[thetutlage]

Hey, the tests are failing coz there are styling issues. https://github.com/adonisjs/ally/pull/120/checks?check_run_id=2704363449

Just run npm run format and then push the code

[Mesteery]

Yes, I saw that the CI failed. However, in local the tests pass.

[thetutlage]

Did you try to run npm run format and see anything change?

[Mesteery]

Yes, there are no change. Also, my branch is up to date with the remote.
I'll retry anyway.

[Mesteery]

It worked (on my another machine), I don't understand why it didn't work before. Sorry.

[thetutlage]

Looks good. Thanks for the PR :)