feat: add the GitLab Duo chat as Vue2 application

This MR, essentially, does two things:

• Updates the build/watch process to include the webviews located in webviews/vue2 (!1007 (b4f1fac5))
• Creates a copy of the current GitLab Duo chat app (in webviews/vue) to webviews/vue2 and adjusts it to be a proper Vue2 application (!1007 (a488be94))

The build/watch jobs have been updated to build GitLab Duo chat from the Vue2 version. Once we have this MR merged and tested, we can remove the Vue 3 copy in a follow-up MR.

Current snapshot of the chat app in the extension:

Related to #994 (closed)