Automatically install dependent collection

[berndfinger]

We could automatically install dependent collections when installing the collection from Ansible Galaxy. See also #552.
Pros:

• No need to manually run the command ansible-galaxy install -vv -r meta/collection-requirements.yml before using the collection

Cons:

• The dependent collection(s) will likely install more dependent collections.
• The dependencies might not exist for all platforms, and installing a dependent collection which is not used might not be accepted by all users.
• A collection can currently not be removed by using the ansible-galaxy command but only by removing directory trees, see this section of the Ansible "Installing collections" guide. This is a bit uncomfortable and more error-prone than with a command option.