Revisit Gripper API

[TomCC7]

Requirements:

1. need to support both absolute and normalized gripper api for motion planning and learning usage
2. support multi-finger gripper
3. (might be related to robot_id stuff) on hardware interface level gripper might be controlled from either robot sdk or dedicated adapter, and we need to support both case but provide unified upstream api

Ideas on API:

1. should expose normal joint control interface similar to robot joints (either prismatic/rotational)