[Feature] Add a de-noising step to `preprocess`

[K-Meech]

Is your feature request related to a problem? Please describe.
As outlined in our summary issue: brainglobe/atlas-forge#10, we wanted to have a de-noising step as part of the raw_to_ready preprocess pipeline.

Describe the solution you'd like
We need to decide which filters we want to support, and what settings would need to be added to the config file e.g. some atlases have previously used a median filter for this step. We also need to decide if this is available as an alternative option to the bias field brightness correction, or whether it is another step in addition to this.

Related to brainglobe/atlas-forge#10, brainglobe/atlas-forge#14

[niksirbi]

Now that we depend on simpleitk, I wanted to just mention that the whole catalog of sitk filters is open to us, should we ever want something from that list.