This commit changes the way that depends_on blocks are parsed and
tracked during the `podman-compose up` process.

Each service's dependencies will be tracked as a dict in which keys are
services being depended on and values are the condition to be met by
said services before the current service can start.

This lays the groundwork for supporting long-syntax / conditional
depends_on blocks, but should not change any behavior so far.

Signed-off-by: Adrian Torres <atorresj@redhat.com>

This commit implements the long-syntax / conditional depends_on compose
mechanism which instructs the compose system to wait for a certain
condition before starting a container.

Currently available conditions are:

- service_started: same behavior as before this commit, the depending
  container will start as soon as the depended on container has started
- service_healthy: if the depended on container has a healthcheck, wait
  until said container is marked as healthy before starting the
  depending container
- service_completed_successfully: wait until the depended on container
  has exited and its exit code is 0, after which the depending container
  can be started

This mechanism is part of the v3 [1] compose spec and is useful for
controlling container startup based on other containers that can take a
certain amount of time to start or on containers that do complicated
setups and must exit before starting other containers.

[1] https://red.ht/conditional-depends

Signed-off-by: Adrian Torres <atorresj@redhat.com>

Co-authored-by: Dawid Dziurla <dawidd0811@gmail.com>