Update docs for Gitpod support

Created by: abeatrix

Close https://github.com/sourcegraph/sourcegraph/issues/35215

Also updated the format for the Editor Integrations page:

Before	After

Note: Currently using the steps from https://github.com/sourcegraph/sourcegraph/issues/35494 on installing the extension on Gitpod Browser (which is using VS Code Web). If we decide to host the extension somewhere, we can just update step 1 with the URL where we are hosting the VS Code Web extension

Test plan

manually run through the installation steps