hwp-supervisor: Add shutdown delay flag

[bbixler500]

Description

Adds a configurable parameter for the delay between the supervisor shutdown and the pmx/gripper shutdowns

Motivation and Context

As part of the supervisor shutdown, the bias power to the HWP driver board is turned off. When this happens the frequency readout of the HWP drops to zero, even if the HWP is still rotating. This might be confusing for someone not familiar with the HWP so we've decided that the supervisor shutdown should be delayed relative to the other HWP agent shutdowns

How Has This Been Tested?

This was tested with SATp1 while it was partially warmed up for the HWP rotor recentering

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[ykyohei]

This looks great. thanks for making this and testing this!