Enable the static delta computation between specific commits

[lubosmj]

Right now, we compute the static delta between the last two commits. We can enhance this feature by enabling the users to choose which commits they want to compute the delta between.

I am referencing the old issue: #230 deltas_upto was not considered in the implementation back then.

[lubosmj]

Do we want to expose a new endpoint that accepts two commits/repository versions?

[lubosmj]

Do we want to compute the static delta beforehand for all versions automatically?