Auto-update: Generate release metadata

[timtmok]

Positron needs an endpoint to retrieve the current release metadata. This will be used to compare with the running version to determine if a newer Positron version is available. The release metadata can be stored with each platform and architecture and is updated with each new published build.

• Create a JSON file for each platform and architecture that contains the current release version and a URL where it can be downloaded
• Create a staging area for builds

Release metadata structure:

{
  "url": "<url to 2024.12.0 release>",
  "name": "2024.12.0",
  "version": "2024.12.0",
  "productVersion": "2024.12.0",
  "sha256hash": "fe01f564777afb75703e748ada00f1204f0495be54947d6ffb513e5a5eb16a08",
  "timestamp": 1731509492275,
}