change date separator in filenames to '-', update bounds metadata

[klindsay28]

bounds metadata mods fix ESCOMP/MOM_interface#107

New time and time:bounds metadata is

    double time(time) ;
      time:units = "days since 0001-01-01 00:00:00" ;
      time:long_name = "time" ;
      time:axis = "T" ;
      time:calendar = "noleap" ;
      time:bounds = "time_bounds" ;

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

The date separator change goes with PR to https://github.com/ESCOMP/MOM_interface,
so that files with changed names get archived by short-term archiver and testing baseline generation works.
Once that PR is submitted, I will update this PR with a link to it.

[jedwards4b]

Thank you Keith - should this PR be marked as draft until the MOM_interface PR is submitted or can it be merged first?

[klindsay28]

Corresponding MOM_interface PR is ESCOMP/MOM_interface#144

[klindsay28]

The merging of this PR should be coordinated with the merging of the MOM_interface PR.
If one runs with this PR and not the MOM_interface PR, MOM6 output will not get archived by the short-term archiver.

[klindsay28]

I don't appear to have permission to suggest reviewers, so I'm writing here to state that this PR is ready for review.