Improve gazebo/igntion import procedures.

[nuclearsandwich]

Raised by @chapulina in #113
It would be nice to improve this process 🙃 I actually don't know if just pulling ign-cmake2 will be enough, so this may not even be the end of this round.

The only suggestion I have is to always pull the latest versions of all libraries (abuse those globs!). I know there's a desire to keep track of what exact versions are being imported, but as noted along this series of PRs (#109 / #110 / #111 / #112), the versions listed on this file aren't accurately reflecting the state of the server.

If we always pull the latest versions:

• We're sure they all work together, because that's actively tested by the Ignition team
• We don't need to edit this file every time we need to make an upgrade (saves time)

[j-rivero]

The current import approach is not able to check for version constraint dependencies (not in aply CI at least as of today). This can lead to problems like the one raised in gazebosim/gz-cmake#304, that appears when a new version constraint is introduced in an update to a given package for reprepro.

[j-rivero]

The CI is not checking if explicit version exists #166 (comment)