Introduce --wait or --watch capabilities to **depends_on**, avoiding configuration of healthchecks for simple use cases

[esauvisky]

Description

Sometimes, we need to wait a bit after launching a container before starting a container that relies on it, as services may take time to boot up. The proper approach is to set a healthcheck and use that as the sign that the dependency is genuinely ready for the dependent service to start. However, healthchecks can be quite complicated and hard to implement in every case, making it much easier if we could just pause for a few seconds before starting the dependent service.

With the introduction of the (relatively) new features --wait and --watch, I propose we expand their capabilities to include the depends_on feature.

[tchavei]

Indeed that would be a excellent quality of life improvement. I have several containers that "depend on" other containers but sometimes they still start too quickly before the preceding container finishes loading the app. A timer or delay would be invaluable.

Great idea!