Move packages to gz and add ignition alias

[chapulina]

• Part of Debian packages from ignition to gz gazebo-tooling/release-tools#736
• Redo of Initial implementation for gz- alises #1

This PR fixes the issue identified with #1 by adding Breaks / Replaces rules so the new packages replace the old ones.

After 7b12d8e:

Downstream CI for utils:

[chapulina]

Build is green, and installing the new packages on top of old ones works well locally.

The test utils Jenkins run also did the right thing:

The following package was automatically installed and is no longer required:
  libignition-cmake3-dev
Use 'apt autoremove' to remove it.
The following NEW packages will be installed:
  libgz-cmake3-dev