Add Positron manifest

[cderv]

I managed to make a manifest for it in current state despite

• https://github.com/posit-dev/positron/issues/3703

We'll adapt later a .7z or .zip version is available

[github-actions[bot]]

All changes look good.

Wait for review from human collaborators.

positron

• [x] Description
• [x] License
• [x] Hashes
• [x] Checkver
• [x] Autoupdate
• [x] Autoupdate Hash Extraction