feat: Add GitHub Pull Request extension to workspace template

[tyler36]

The Issue

No GitHub Pull Request extension was included in the workspace setup.

How This PR Solves The Issue

This update adds the GitHub Pull Requests extension to the workspace documentation and the user-defined web template.

Coder uses GitHub for authentication so it make sense to include a helper extension for GitHub.

Manual Testing Instructions

Verify that the GitHub Pull Requests extension is listed in the workspace documentation and the template file.

Automated Testing Overview

No automated tests are needed for this change.

Related Issue Link(s)

Release/Deployment Notes

No additional deployment steps are required.

[rfay]

I'm a little worried about infinite extension requests as in

• A few more suggestions for extensions to add to VSCode #42

Each costs a second or two at workspace startup time, you can see them happen as the logs go by.

[tyler36]

I'm a little worried about infinite extension requests as in

Yes, thats a fair call. Almost every project I use interacts with GitHub. However, only my Javascript projects use Eslint.

If we are worried about startup, I think we should strip them back to bare minimal

• remove all the linting extensions
• keep PHP Debug
• keep DDEV manager (although I find myself more comforable using the CLI)
• include GitHub Pull Request (this PR)

[rfay]

What's happening though is just hitting each person's favorites, without a clear path. I personally haven't enjoyed the GitHub pull request extension, prefer the web UI and gh.