Only allow Sourcegraph authored extensions

Created by: ryankscott

We've had a number of requests to only allow extensions created by Sourcegraph as users are concerned about the likelihood of installing malicious extensions.

As part of this we also need to define what are "Sourcegraph authored" extensions.

Product Gaps

• Only allow extensions created by Sourcegraph

Productboard feedback

• Only allow extensions created by Sourcegraph