Add new optional XML element for dimension names

### What is the feature/what would you like to discuss?

In the generated namelists for physics, dimensions are named `_dimension` (with number suffixes if there are more than one dimension).

That is not very standard-name-compliant. As noted by @nusbaume, it'd be preferable to include a new (optional) XML element to specify the name(s) of the dimension(s) of the namelist variable

### Is there anyone in particular you want to be part of this conversation?

_No response_

### Will this change (regression test) answers?

No

### Will you be implementing this enhancement yourself?

Any Software Engineer can do this