Improvements to compose file scaffolding

[bwateratmsft]

We discussed what we want for a user experience for Compose scaffolding.

• Ability to add services to already-scaffolded compose files for all platforms (one service at a time)
  • Choose which compose file(s) to add the service to--allowing support for having many different compose files that launch different groups of services
• Multiple-platform support, e.g. a compose file that references both .NET and Node projects
• Samples for external services (e.g. database) that aren't being built (maybe best done in language server, Add intellisense for docker compose files #2539)

[bwateratmsft]

Moving to future per our discussion. We'll await user feedback.

[ucheNkadiCode]

Adding specific note: Inserting snippet to add a "well known" service/image within a compose file. (Redis, postgres)

[bwateratmsft]

Probably the best way to do that would be with the language server. I'll put a checkmark for it. #2539

[bwateratmsft]

Basically covered by #2539 so I'm going to close this one.