Docs: add explanation and example strategies around affected and lock files

[blordpluto]

Documentation issue

• Documentation improvement

@meeroslav This was promised last year, still hoping to see it soon. 😄 See:

#15116 (comment)

In general, the relationship of the dependency graph to lockfiles feels underdocumented across the entire project. This is a major topic and deserves a bit more IMO. Thanks!