e2e Test: Add automated tests for Auto update

[jonvanausdeln]

Need to add automatic update tests.

See https://connect.posit.it/positron-wiki/auto-update.html

Scenarios to be tested:

• Default check, but no auto update - just verify new update is available at startup
• Manual check, no auto update - verify that use is notified only when manually checking
• Auto download
  • Only available on Windows and MacOS
  • Windows allows download and manual install as well as backgound update (download & install)

Most likely need a build with a distant build number to push to the staging S3 bucket and test will verify against it.