Add kestrel as an exec option

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (8ad8c9d) 87.01% compared to head (96c3ad5) 87.06%.

Files	Patch %	Lines
reV/config/execution.py	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #434 +/- ## ========================================== + Coverage 87.01% 87.06% +0.04% ========================================== Files 122 122 Lines 17016 17029 +13 ========================================== + Hits 14807 14826 +19 + Misses 2209 2203 -6 ``` | [Flag](https://app.codecov.io/gh/NREL/reV/pull/434/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/NREL/reV/pull/434/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL) | `87.06% <0.00%> (+0.04%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL#carryforward-flags-in-the-pull-request-comment) to find out more.

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