[develop] Replace existing UW CLI with UW API calls for template

[elcarpenterNOAA]

DESCRIPTION OF CHANGES:

This PR continues the integration of the uwtools package by replacing current use of the UW CLI with UW API calls in Python scripts. These changes are limited to the template tool.

Type of change

• New feature (non-breaking change which adds functionality)

TESTS CONDUCTED:

• hera.intel
• orion.intel
• hercules.intel
• cheyenne.intel
• cheyenne.gnu
• derecho.intel
• gaea.intel
• gaeac5.intel
• jet.intel
• wcoss2.intel
• NOAA Cloud (indicate which platform)
• Jenkins
• fundamental test suite
• comprehensive tests (specify which if a subset was used)

DEPENDENCIES:

n/a

DOCUMENTATION:

None. UW Documentation is up-to-date.

CHECKLIST

• My code follows the style guidelines in the Contributor's Guide
• I have performed a self-review of my own code using the Code Reviewer's Guide
• 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 do not require updates to the documentation (explain).
• My changes generate no new warnings
• New and existing tests pass with my changes
• Any dependent changes have been merged and published

[elcarpenterNOAA]

These same simplifications are repeated throughout these 5 files.

[christinaholtNOAA]

I think values_src wants a Path object here (and elsewhere).