[master] deb/rpm define dependencies between docker-ce-cli and docker-compose-plugin

[thaJeztah]

Follow-up to #553

With this change, the compose-cli-plugin will automatically be installed as dependency of the cli.

deb: add docker-compose-plugin as "recommends"

This adds a "weak" dependency on the docker-compose-plugin, per the
recommendations in https://debian-handbook.info/browse/stable/sect.package-meta-information.html#id-1.8.6.7.10.10

The "recommends" dependency will be installed by default, but does allow users to opt-out
using --no-install-recommends to perform a lightweight installation for setups that only
need basic functionality of docker;

(...) the “recommended” dependencies, the most important, considerably improve
the functionality offered by the package but are not indispensable to its operation.
(...) You should always install the “recommended” packages, unless you know exactly
why you do not need them. This is now also the default for APT unless configured
otherwise.

rpm: add docker-compose-plugin as "recommends" / "requires"

This defines the dependency between the docker cli and compose (as a plugin). RHEL8
and CentOS 8 (and up) support weak dependencies;

• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/packaging_and_distributing_software/new-features-in-rhel-8_packaging-and-distributing-software#support-for-weak-dependencies_new-features-in-rhel-8
• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/packaging_and_distributing_software/new-features-in-rhel-8_packaging-and-distributing-software#boolean-dependencies-syntax

But CentOS 7 and RHEL 7 do not yet support this, so for those, we use "Requires",
using the %rhel macro for detection, which also works on CentOS:

rpm --eval '%{rhel}'
7

Making the dependency recommended will install it by default, but users are able
to opt-out explicitly, using --setopt=install_weak_deps=False, for example, to
perform a light-weight installation that does not require all features of Docker.