Branch off for Galactic

[chapulina]

We're ready to default to Fortress for Rolling. Since bloom doesn't allow the injection of custom environment variables (see ros-infrastructure/bloom#517), the release will always take the default conditionals on package.xml and CMakeLists.txt. This means we need to branch off just so each branch defaults to a different version:

• galactic defaults to Edifice
• ros2 (rolling, future humble) defaults to Fortress

Desired behavior

The galactic branch can be released using Edifice and the ros2 branch can be released using Fortress.

Alternatives considered

I can't think of anything besides bloom allowing the injection of environment variables, or another way of passing parameters.

Implementation suggestion

• Create the galactic branch off ros2 and enable branch protection
• Open PRs for all versions updating the README with the new branch
  • melodic: [melodic] Update docs for ros2 branches #202
  • Merge melodic to noetic
  • galactic: also remove Rolling support: Separate galactic branch from ros2 branch #201
  • foxy: [foxy] Update docs for ros2 branches #203
  • ros Update Default to Fortress for Rolling (future Humble) #195 so the ros2 branch is only for Rolling
• Make a new release of galactic and update the rosdistro branch to galactic
  • ros_ign: 0.233.3-1 in 'galactic/distribution.yaml' [bloom] ros/rosdistro#31644
• Make a new release of ros2 for Rolling using Fortress
  • ros_ign: 0.244.0-1 in 'rolling/distribution.yaml' [bloom] ros/rosdistro#31645

Additional context

Previous tickets which provide more context:

• Default to Edifice for Rolling #150
• Status of Foxy branch #162