Allocate hist_coords to max dimensions rather than arbitrary limit

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

In `src/history/cam_history_support.F90`, we have:
```
integer, parameter :: maxmdims = 25 ! arbitrary limit
type(hist_coord_t), public :: hist_coords(maxmdims)
```
Instead, as pointed out by @nusbaume in https://github.com/ESCOMP/CAM-SIMA/pull/274, we should determine the biggest number of dimensions that were needed (based on the user_nl_cam history variables configured), and have the maxmdims value set to that (with hist_coords then an allocatable variable that is allocated to that size)

### 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