boulder: Add a marker in manifest.bin for what version of boulder it was built against

[joebonrichie]

In CI/Infra checks we can then warn/error if the boulder is too old/doesn't match. Macros do exist as plain text on the system so maybe a sha of the macros directory should be included in the marker as well.

[ermo]

Requires versioned repos, which requires Rust infra, hence scheduling for alpha3.

Great idea!