MuSR: separate Danfysik into low and high slew rate components

As a MuSR instrument scientist I would like my Danfysik IOC in the base component to be separated into a `low_slew_rate` and `high_slew_rate` component with different slew rates set on each (these can be found in the musr_routines.py script on MuSR.) I would then like the components to be included in the respective configurations.

This can probably replace #6287 as it requires a config architecture change rather than a change in the blockserver.

Acceptance criteria
- Danfysik is split up from being in the base component into a low and high component
- These low and high components are included into the triton configurations where needed (which can be found in the `setmag()` script currently)
- The part of the script in `setmag()` in `musr_routines.py` which sets the slew rate per config name is removed as it will be superfluous