Ingester: reject checkouts without commit_hash

Even though all checkouts should have a commit hash by default, it is still possible for maintainers to submit such results, and the database allows this case. The commit_hash is a very important field since it is used for accessing the treeDetails page and also navigating between commits, it should be enforced to be not null and wrong data should be rejected.

Comes from a [comment](https://github.com/kernelci/dashboard/issues/1436#issuecomment-3265900088) on another issue, but was born from wanting group builds and tests with some key fields (https://github.com/kernelci/dashboard/issues/1454)

Start by tracing the Ingester checkout submission path and the database schema for commit_hash, then inspect existing validation and tests around checkout results. Done means submissions without commit_hash are rejected and the database no longer permits null values for this field.

Written by the indexing model from the issue text.