Correction to how Savanna action digest is computed

[arhag]

Correction to changes from AntelopeIO/leap#2326 to implement AntelopeIO/leap#2161.

We want the rest of the metadata of the action receipt that are not the first five fields in AntelopeIO/leap#2161 (comment) to be captured in a separate hash. That way for IBC purposes the remainder of that metadata does not need to be provided as part of the proof; instead a single 32-byte digest can replace them for the purpose of the proof.