[feature] 'clean-modified' command for bundle files

[GordonJess]

Same use case as conan lock clean-modified.

When I send a bundle to an agent for building a package, I'd like to be able to remove all modified flags (in the bundle file and all lockfiles) to know exactly which nodes were modified by this agent.

Currently need to parse the bundle file and get a list of lockfiles to run conan lock clean-modified on each (the parsing is not so clean due to the way it is structured).

[memsharded]

Proposing #8726 for 1.35