Add option to collect and save provenance data helpful for tracking what was used in a build

[lionel]

Stuff like the defconfig name, the hash of distro-seed and of the kernel, and of other repositories and other "goes-intos" that are soon lost and/or forgotten. Especially when trying to figure out years down the road what went into producing an image.

[ts-kris]

This isn't a bad idea, but some of this already exists in the output image itself (which, IMO is better than a separate file that gets generated, but that doesn't mean a separate file shouldn't be generated).

Kernel hash should be encoded in uname
Most utils packages have their git hash built in*
The actual distro-seed hash AFAIK isn't saved anywhere but would be a nice to have.

(*) The way they are grabbed can be weird depending on how they are grabbed. e.g. with Buildroot, the utils actually end up taking on the hash of the Buildroot repo. I'm not sure what distro-seed ends up with at this time.

[ts-kris]

Also, since I'm catching up, this looks like it might be a dup of #45.

[lionel]

Watching #45, but I haven't been able to verify all relevant meta-data, e.g. hashes of the kernel and tools.

[lionel]

With distro-seed, I'm not seeing the kernel git hash encoded in the uname like it was with 4.9/debian-seed for the TS-71x0 boards. At least in 4.9, the setlocalversion script was involved, IIRC.

[lionel]

For "tracing back" to find out what kernel, ts7100-utils, or whatever went into a rootfs, it wasn't clear we needed or wanted that information in the rootfs itself, but rather to hold it back so we have a clue to reference when we're starting with limited information. Also, if some component doesn't come from a public repository, not all useful information may belong in the final image.