Enable reproducible environments

[ctcjab]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

conda-build should allow users to provide a conda-lock lockfile so that it can create environments in a reproducible fashion when building (and optionally testing) a package.

Why is this needed?

Because conda-build does not currently support lockfiles, running the same conda-build command on the same revision of a codebase can succeed the first time you run it and fail the second time you run it, due to out-of-band changes (e.g. a transitive dependency publishing a new version). This makes conda-build users' CI jobs unreliable, and makes it harder to find out why a build has broken. If conda-build consumed lockfiles that were versioned in the codebase, it would enable the invariant that every CI job's pass/fail result is a pure function of the revision of the code that it ran against, and so if revision X passed and revision Y failed, the cause of the failure can be found somewhere in the diff between revision X and revision Y.

What should happen?

conda-build should allow users to provide lockfiles which it should use for every environment that it creates as part of the build, bypassing solver-based non-determinism.

Additional Context

No response