Delay startup till dependencies ready

Nobody has claimed this yet.

### Problem description
Many services require dependencies (databases, async comm facilities etc.) to be available to do any work. While it is ultimately required for robust services to be resilient when dependencies are missing or misbehaving, starting everything at once and relying on health checks/retries unnecessarily slows down the startup and results in a lot of noise in the logs.

Aspire customers have been using and recommending https://github.com/davidfowl/WaitForDependenciesAspire and experimenting with it (e.g. https://github.com/afscrome/WaitForDependenciesAspire fork) which shows this is an unmet need.

### Use cases
- Wait till dependency has successfully started
- Wait till dependency service is ready to serve traffic (endpoint created)
- Wait till dependency is healthy
- Wait till dependency is done running (ran successfully) -- e.g. for database seeding

### Related issues
https://github.com/microsoft/usvc/issues/69 (the health check feature) will be required for "wait till dependency is healthy" use case.

Review the DCP API server and CLI context, then examine the related health check issue and the referenced WaitForDependenciesAspire projects for the dependency-readiness behavior described here. Done should cover the applicable startup, endpoint, health, and successful-completion waiting use cases without relying on broad retry noise.

Written by the indexing model from the issue text.