Modify naming and attributes of time variables on history files to be consistent with other CESM components

These changes are being requested to improve the ease-of-access of CESM data and to normalize the look of the metadata across CESM components. See https://github.com/ESCOMP/CESM/issues/194 and especially the google doc referenced from https://github.com/ESCOMP/CESM/issues/194#issuecomment-961443965.

Current CISM time array output:

double time(time) ;
time:long_name = "Model time" ;
time:standard_name = "time" ;
time:units = "common_year since 0000-01-01 0:0:0" ;
time:calendar = "noleap" ;

Proposed CISM time array output:

double time(time) ;
time:long_name = "time" ;
time:units = "days since 0001-01-01 00:00:00" ;
time:calendar = "noleap" ;
time:bounds = "time_bounds" ;
double time_bounds(time, nbnd) ;
time_bounds:long_name = "time interval endpoints" ;
time_bounds:units = "days since 0001-01-01 00:00:00" ;
time_bounds:calendar = "noleap" ;

Changes made: Add time_bounds variable, alter time@units to match other components, add time@bounds, remove time@standard_name, change time@long_name to “time”.

@billsacks @phillips-ad @strandwg are filing similar issues for each component.