make reproducible-prestate affected by untracked files

[pauldowman]

make reproducible-prestate gives a different result if there are untracked files in the repo. It's expected that this would happen if there are custom rollup configs in op-program/chainconfig/, but it also happens with other files, e.g. in op-service which should not happen.

[sebastianst]

One solution is to run a git command at the start to find all changed and untracked files and print a warning that those may influence the prestate hash.

[ajsutton]

Just to bring other conversations together here - we do expect that untracked files will cause the prestate to differ. We should:

1. ensure that anything that is git ignored doesn't affect the result
2. Update any instructions for building prestates to ensure they tell people to confirm they have no outstanding changes (ie git status reports no changes and no untracked files). A lot of instructions already start by saying to check out the repo so that's not an issue.
3. Consider Seb's suggestion above of logging a warning if there are changes. We should do that at the end of the build so it's output next to the printed absolute prestates. It will get lost if we print it at the start.