VSCE: Add open-vsx release step

Created by: abeatrix

Add open-vsx release step to release pipeline

Test plan

Tested locally.

Passing integration test - 7/6:

VSCode started in debug mode on http://127.0.0.1:29378
    ✓ works (10063ms)


  1 passing (27s)

✨  Done in 33.78s.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.