Bugfix: Enable "Follow ..." feature when the tablet is attached

[hello-amal]

Description

Currently, the "Follow Gripper" feature is broken when the tablet is attached, because it is looking for the link_gripper_finger_left TF frame, which doesn't exist.

This PR addresses that with the following:

1. Creates a ROS param that the web app has access to, which contains the tool. (Note that although there is a topic, /tool, that publishes this info, a ROS param reduces the number of messages that need to pass through RMW's wait set, particularly since this information is only needed once).
2. Changes the label of the button to "Follow Tablet" if the tool is the tablet, "Follow Gripper" if it is one of the grippers, else "Follow Wrist."
3. Change the TF poses it is following to be link_DW3_tablet_12in, link_gripper_finger_left, or link_wrist_yaw respectively, for each of the cases above.

Testing procedure

• [x] Disconnect the Dex wrist and D405, attach the tablet, and run stretch_configure_tool.py. Choose the tablet.
• [x] Run the web interface, verify the button is "Follow Tablet" and it works as expected.
• [x] Re-run stretch_configure_tool.py, and choose nil.
• [x] Run the web interface, verify the button is "Follow Wrist" and it works as expected.
• [x] Re-connect the dex wrist and D405, and run stretch_configure_tool.py.
• [x] Run the web interface, verify the button is "Follow Gripper" and it works as expected.

Before opening a pull request

From the top-level of this repository, run:

• [x] pre-commit run --all-files

To merge

• [ ] Squash & Merge