Drawdown Parameter Schedule [v.3.13.12]

[softwareengineerprogrammer]

Description

1. Add Drawdown Parameter Schedule
2. Add example4_drawdown-schedule
3. TODO:
   1. Minor version bump: 6a0b7fa, 383906e
   2. CHANGELOG entry
   3. 🚧 Web interface

Testing & Verification

1. Unit tests added:
   1. example4_drawdown-schedule
   2. test_drawdown_parameter_schedule
2. Unit tests updated: N/A
3. Manual testing:
   1. Manually tested & reviewed

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Change Checklist

Observe the following checklist items before and after merging, as applicable.

Before merging:

1. I certify that I am a human and I have manually verified the correctness of the changes in this PR.
2. Add a CHANGELOG entry if your change includes a new version¹ (example). RST Template:

M.m.P: `TITLE <https://github.com/NREL/GEOPHIRES-X/pull/PR-NUMBER>`__ | `release <https://github.com/NREL/GEOPHIRES-X/releases/tag/vM.m.P>`__

After merging:

1. Push tag(s) to GitHub: git push origin refs/tags/v3.13.12
2. Post a change announcement to the GEOPHIRES Change Announcements Discussion (example). Markdown template:

3.13.12: [TITLE](https://github.com/NREL/GEOPHIRES-X/pull/PR-NUMBER) | [release](https://github.com/NREL/GEOPHIRES-X/releases/tag/v3.13.12)

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Self-reviewed in #166

Footnotes

1. See versioning notes and version management docs. ↩