Diff: database storage for calculated diff

[ajtmccarty]

Component

No response

Describe the Feature Request

New components to store and retrieve calculated diffs to/from the database. Using the new data structures introduced in #3280.

The new datastructure is easy to transform into a graph and should be easy to store and retrieve with Cypher

Describe the Use Case

Once a diff a calculated for a given base_branch, diff_branch, from, and to, it will never need to be calculated again, so we can skip the processing time for calculating it by saving it to the database and retrieving it

Additional Information

No response