Add CUSTOM_COMPILE_COMMAND support to uv pip compile (#2554)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
This adds support for `CUSTOM_COMPILE_COMMAND` support to change the
header comment in generated requirements files.
See Issue:
- #1527
From [pip-tools docs](https://pip-tools.readthedocs.io/en/latest/):
> You might be wrapping the pip-compile command in another script. To
avoid confusing consumers of your custom script you can override the
update command generated at the top of requirements files by setting the
CUSTOM_COMPILE_COMMAND environment variable.
## Test Plan
<!-- How was it tested? -->
See unit test included
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Co-authored-by: konsti <konstin@mailbox.org>
