Set GAAS offset to CHEMISTRY_DT

[mathomp4]

NOTE: PR summary below thanks to Copilot :)

---

This pull request includes updates to ensure the GAAS_GridComp_ExtData.yaml file's update_offset matches the CHEMISTRY_DT value from CAP.rc. The changes involve extracting CHEMISTRY_DT, converting it to ISO duration format, and updating the update_offset in the YAML file accordingly.

Updates to GAAS_GridComp_ExtData.yaml:

• Added code to extract CHEMISTRY_DT from CAP.rc, convert it to ISO duration format, and update the update_offset in GAAS_GridComp_ExtData.yaml in gcm_run.j.
• Added similar code for updating GAAS_GridComp_ExtData.yaml in gcm_forecast.tmpl.
• Added code to move and modify GAAS_GridComp_ExtData.yaml in gcm_run_benchmark.j.
• Added code to update GAAS_GridComp_ExtData.yaml with CHEMISTRY_DT in gcm_run_benchmark.j.