VSCE: Add open-vsx publishing step to auto release pipeline

Created by: abeatrix

We have recently published VSCE to Open VSX

Dev exp team helped create an access token using the @soucegraph-bot account for future vsce release to the open vsx registry. We should add the publishing step to our existing vsce auto release pipeline

Ref: https://sourcegraph.slack.com/archives/C01CSS3TC75/p1656045575021719