[ign ➡️ gz] Clone directories

[chapulina]

• Part of Rename Ignition to Gazebo release-tools#698
• Broken off ign ➡️ gz #109
• Goes with [ign ➡️ gz] Update VCS directory for Windows CI release-tools#738

This PR is migrating only the directory name when a repository is cloned.

Commands run:

sed -i 's/ign-\(.*\):/gz-\1:/g' *.*
sed -i 's/gz-gazebo/gz-sim/g' *.*

Tests

This may affect CI, I'll run some tests before opening for review.

• Windows CI (which uses gazebodistro via vcs + colcon):

[methylDragon]

Are we going to need to migrate the branch names eventually.. 🤔

[chapulina]

Are we going to need to migrate the branch names eventually..

Not the ones that are currently stable. Nor the existing tags. That's to keep backwards compatibility. But new branches and tags will be gz.

[j-rivero]

Let's follow in #117