Add two new time filters to jinja

[DavidHuber-NOAA]

Description
This adds the timetools functions to_timedelta and add_to_datetime to the jinja filter list.

Here's an example of how to use the new filters:

{% for restart_offset in ["+3", "+6", "+9"] %}
{% set restart_delta = restart_offset | to_timedelta %}
{% set restart_datetime = current_cycle | add_to_datetime(restart_delta) %}
{% endfor %}

Needed for NOAA-EMC/global-workflow#2491

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• pynorms
• pytests

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes need updates to the documentation. I have made corresponding changes to the documentation
• My changes generate no new warnings
• New and existing tests pass with my changes

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 47.84%. Comparing base (c237f19) to head (cdc9751).

Files	Patch %	Lines
src/wxflow/jinja.py	33.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #25      +/-   ##
===========================================
- Coverage    47.90%   47.84%   -0.06%     
===========================================
  Files           18       18              
  Lines         1647     1649       +2     
  Branches       333      335       +2     
===========================================
  Hits           789      789              
  Misses         801      801              
- Partials        57       59       +2     

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[aerorahul]

looks good.
Would you mind putting in the PR description what the template would look like for posterity?

[DavidHuber-NOAA]

Sure thing. Done.