Enhance curriculum design and management instructions

[SimmonsNeudesic]

Improve curriculum management by adding comprehensive guidelines for curriculum mapping, audience targeting, and content updates. Include detailed prompts for gap analysis, relevance assessment, and effective prompt creation to ensure alignment with learner needs and organizational goals.

[SimmonsNeudesic]

@dinmanchi @karthik00678 @derekhuynen

This is the result of the conversation the other day about having an agent help to keep the repo updated.

This adds a custom chatmode (agent): "curriculum-designer"

It adds several prompts for the curriculum-designer to work with:
/generate-curriculum-map -> Creates or updates a curriculum map metadata file based on the repo documentation and lessons
/generate-target-audience -> Creates or updates a target audience metadata file based on user interview or prompt context
/identify-curriculum-gaps -> Compares "what we teach" (curriculum map) with "who we're teaching" (target-audience) to see places we need to improve
/search-for-updates -> Gets the latest updates from Github Copilot and VS Code release documentation for analysis and potential inclusion for the content. (makes metadata file "proposed-changes.md")

Search for updates prompt also adds the github issues to the repo for the content.