[Enhancement] Introduce 'head' parameter for snapshot validation.

[ruseinov]

Summary of changes

Changes introduced in this pull request:

• Introduce HEAD param to make sure we can specify ranges when importing and validating a snapshot.

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[ruseinov]

A follow-up issue: sort out snapshot validation parameters interface as it's quite confusing.

[lemmih]

Using i64 (or ChainEpoch) might be easier.

[ruseinov]

Using i64 (or ChainEpoch) might be easier.
I agree that it's not the most eloquent of solutions.

It makes no sense to accept i64 though as we don't want to allow negative values for this one. Hence the u64.
In an ideal world we should have validation for this and all the other CLI params. Perhaps a good issue to create for when we'd want to re-vamp and move those out of the daemon?