add timestamp to rpointer files

[jedwards4b]

Description of changes

Adds a timestamp to rpointer files in a backward compatible manor

Specific notes

Contributors other than yourself, if any:

CTSM Issues Fixed (include github issue #):

Are answers expected to change (and if so in what way)?
no
Any User Interface Changes (namelist or namelist defaults changes)?

Does this create a need to change or add documentation? Did you do so?

Testing performed, if any:
(List what testing you did to show your changes worked as expected)
(This can be manual testing or running of the different test suites)
(Documentation on system testing is here: https://github.com/ESCOMP/ctsm/wiki/System-Testing-Guide)
(aux_clm on derecho for intel/gnu and izumi for intel/gnu/nag/nvhpc is the standard for tags on master)
ERR_Ln9_C3.ne30pg3_ne30pg3_mg17.FLTHIST.derecho_intel.cam-outfrq9s
NOTE: Be sure to check your coding style against the standard
(https://github.com/ESCOMP/ctsm/wiki/CTSM-coding-guidelines) and review
the list of common problems to watch out for
(https://github.com/ESCOMP/CTSM/wiki/List-of-common-problems).

[wwieder]

Thanks Jim. Can this go onto b4bdev, @ekluzek ?

[ekluzek]

Thanks @jedwards4b.

@wwieder yes this totally makes sense as something coming into b4b-dev. Since, it has backwards compatibility it doesn't need to be coordinated with other CESM tags or externals. So bringing it into b4b-dev and having it go into CTSM main-dev the next time a b4b-dev tag is made (in two weeks) makes a lot of sense.

[jedwards4b]

I've run into an issue here. The clm_timemgr reads its clock information from the restart file on restart - which makes it hard to read the clock to read the restart file. It's also not a requirement to get this from the restart file as the driver has already set the clock.

[jedwards4b]

I have tested with ERS.ne30pg3_t232.BLT1850.derecho_intel.allactive-defaultio
and plan to do a complete set of cesm prealpha tests.

[samsrabin]

We discussed this at the CTSM SE meeting this morning and decided it would be in our cesm3_0_beta04 tag, which fits with @jedwards4b's timeline.