Update 'main' policy in README and fix build status table

[nbbrooks]

No description provided.

[christophfroehlich]

LGTM

[christophfroehlich]

Actually, I see some issues:

• Why is the humble build status removed?
• https://github.com/PickNikRobotics/ros2_robotiq_gripper/blob/main/.github/workflows/README.md is still outdated, I'll completely remove it because it is just maintenance overhead.

[nbbrooks]

Why is the humble build status removed?

There is no CI job for humble at this point, only rolling.

https://github.com/PickNikRobotics/ros2_robotiq_gripper/blob/main/.github/workflows/README.md is still outdated, I'll completely remove it because it is just maintenance overhead.

sgtm, that table is becoming common, would probably be best if a docs.ros.org page just explained these "Build status Documentation Released packages" concepts and what OSRA infra is used, instead of having a bunch of out of sync explanations in 100s of repositories.

[christophfroehlich]

Why is the humble build status removed?

There is no CI job for humble at this point, only rolling.

There are some files in the humble branch, which should get renewed I guess.
https://github.com/PickNikRobotics/ros2_robotiq_gripper/blob/humble/.github/workflows/humble-binary-build-main.yml