Remove mimic tags and rename `sim_ignition` to `sim_gazebo`

[sea-bass]

I was trying to use this package on Rolling / Ubuntu 24.04 and ran into this problem.

Found it was related to https://github.com/ros-controls/ros2_control/pull/1553, in which the <mimic> tags have been deprecated as this information is now looked up directly from URDF.

So these tags, and command interfaces, for mimic joints, should be removed.

---

BTW: This fixes Rolling CI because of a unit test that broke due to the above changes

... though the Coverage build seems to be failing for another reason. Seems to be https://github.com/ros-tooling/action-ros-ci/issues/844

EDIT: fixed in https://github.com/PickNikRobotics/ros2_robotiq_gripper/pull/56

---

I also took the liberty of renaming sim_ignition to sim_gazebo in accordance to my related PR to the Kortex repo: https://github.com/Kinovarobotics/ros2_kortex/pull/228. But I can concede and pull that out to a future PR.

[sea-bass]

It does seem like ros2_control has thrown yet another curveball at us here... I'll take a look later if I can will myself to

[sjahr]

Damn, thanks!

[sea-bass]

This is the PR that broke things -- fixing now https://github.com/ros-controls/ros2_control/pull/1585

Of course, this means that non-rolling CI will now fail, so CI stuff will need to be modified to be on different branches, etc.

I recommend that someone with admin power branch out humble, iron, and jazzy branches and keep those respective distros' CI on those. Then, the top-level README with all the status badges should be updated.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 40.26%. Comparing base (743d20f) to head (2a735e6). Report is 18 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #54 +/- ## ========================================== + Coverage 0.00% 40.26% +40.26% ========================================== Files 5 20 +15 Lines 352 524 +172 Branches 0 33 +33 ========================================== + Hits 0 211 +211 + Misses 352 308 -44 - Partials 0 5 +5 ``` | [Flag](https://app.codecov.io/gh/PickNikRobotics/ros2_robotiq_gripper/pull/54/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PickNikRobotics) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/PickNikRobotics/ros2_robotiq_gripper/pull/54/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PickNikRobotics) | `40.26% <100.00%> (+40.26%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PickNikRobotics#carryforward-flags-in-the-pull-request-comment) to find out more.

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[sjahr]

Thank you @sea-bass !