Propose more focus for web team

Created by: nicksnyder

This PR is in response to two pieces of feedback.

1. The team feels like code insights is buried too deep to be effective for attracting candidates.
2. The web team currently feels like a "bucket/catch all" team that owns too much given its size. This creates a feeling of overwhelm on the team.

The PR proposes a few changes:

1. Explicitly removing web platform work as an ownership area of this team. While this team has done web platform work, it has been incidental and in service to other goals. Especially looking at the documented roadmap, I think we should just be explicit that this team is not functioning as a web platform team today. We need to create that team.
2. Condense "extensions and integrations" into "integrations". This is just a naming change to avoid awkward sentences like "extensions and integrations, and code insights". In this PR "integrations" has bidirectional implications (dev tools integrating with Sourcegraph via our extension API, and Sourcegraph integrating with code hosts via our browser extensions).
3. It lifts the exciting product areas that this team owns to the top of the page, which is the most relevant content to readers outside of the team, including candidates.

I also have an opinion that we should rebrand/rename the web team to "Integrations and code insights" (or, if we are already ready to declare code insights to be a separate team, then rebrand the remaining web team to "Integrations and extensions" or something similar). This change is not implemented in this PR because that would involve a lot of renames.