Update dev containers content

[bamurtaugh]

Updates based on the latest spec, including #5587 and:

• Consider which info to add to spec itself and simply reference from VS Code docs
  • Adding back in pre-build info into VS Code docs, but it may make more sense to be in spec and then we reference the spec from here
  • Enhanced getting started and happy paths
    • Example: clearer usage of build flags like push
  • https://news.ycombinator.com/item?id=32628963
• More content on spec
  • ✅ Adding some more initial info in Update dev containers content #5587
  • Consider more value props and context in these docs and spec
• 🏃 Reference the latest repos and changes
  • New images and features repos, rather than vscode-dev-containers
  • Any other spec content or repos
  • Uppercase for "Features," latest proposals
• ✅ Blog post on Features and images Dev container blog post #5605
• ✅ Remote-try-repos: reference latest images
• ✅ https://github.com/microsoft/vscode-dev-containers issues and PRs - comment with latest plan
• 🏃 containers.dev updates: Updates to /features and /collections pages devcontainers/devcontainers.github.io#29
• Do a pass of spec and containers.dev docs to ensure everywhere uses capital "Features" and other consistency checks

[bamurtaugh]

I believe we've made the most crucial changes for this iteration - moving to backlog to keep this as a tracking issue as other changes emerge.

Notably, documenting the new Templates plans and processes, and removing mentions of vscode-dev-containers will be important.

[bamurtaugh]

Closing as we'll track any remaining items in separate issues.