Adding typescript support for WebOTP API

[plchampigny]

Please fill in this template.

• [x] Use a meaningful title for the pull request. Include the name of the package modified.
• [x] Test the change in your own code. (Compile and run.)
• [x] Add or edit tests to reflect the change.
• [x] Follow the advice from the readme.
• [x] Avoid common mistakes.
• [x] Run pnpm test <package to test>.

If changing an existing definition:

• [x] Provide a URL to documentation or source code which provides context for the suggested changes: (https://wicg.github.io/web-otp/#otpcredential)