This PR introduces numerous updates to both the flow and structure of the workshop, as well as adding new features. Some notes:

• The workshop content is moved to workshop-content from docs. A learner highlighted it looked weird to have a folder called docs listed as being ignored in .copilotignore, as you'd typically want Copilot to look at a project's documentation. It's a small thing, but it allows us to better show proper structure.
• Related to proper structure, the instructions files have been greatly expanded to include ones for different file types and better overarching guidance for Copilot. This is to both drive better suggestions but also provide a good model for creating repos and instructions files. The web project itself has also been made a bit more componentized.
• Added new sections for custom agents and agents page. Rearranged the existing flow to allow for a more natural transition to the latter sections.

Background on two decisions:

• Elected not to include Copilot CLI. This isn't a reflection on the tool, but rather its purpose of allowing a developer to have an agent run autonomously on their desktop. Working in a codespace felt a bit awkward in my experience. Very happy to revisit this, but that's why Copilot CLI isn't included.
• Elected not to include chat modes and other preview VS Code features. Because this workshop is primarily focused on agent development, and the recent flux we've seen on some of preview features, it didn't feel appropriate to include. Again, happy to revisit.