Recommend relevant extensions to use

Created by: slimsag

In the browser extension, I have Use Sourcegraph extensions and enable extensions on the registry enabled.

However, I don't as a user actually know which extensions I should enable, so I end up really just not enabling any.

By large contrast, VS Code aggressively suggests extensions to me when I open new files or projects. (for example, with a "install this extension" alert box); and I usually know the ones they aggressively suggest are high quality because of that. With Sourcegraph, we don't do that, and as such I don't know which extensions are high quality that I should enable.

For context, with VS Code I also do not enable extensions unless they are suggested to me with an alert. I feel that doing so would make my editor buggy due to how many extensions there are which are low quality.

Customers:

• https://app.hubspot.com/contacts/2762526/company/550460939 did not realize they needed to enable the Kotlin extension, better discoverability would have helped