Autodetection of dimensions

[samharrison7]

Users currently have to explicitly specify dimensions. Do we want to add an option to automatically detect dimension size and create a NetCDF dimension accordingly? E.g. the following would create a dimension called x in the NetCDF file with value of 5:

{
  "my_var[x]": [0,1,2,3,4]
}

...instead of having to do:

{
  "dimensions": { "x": 5 },
  "my_var[x]": [0,1,2,3,4]
}