Allow setting arbitrary labels for elements in basic commitment algorithms

[Rumata888]

Commitment algorithms (IPA, KZG) have fixed labels for elements being added to the transcript. If 2 instances need to be used in the same transcript for whatever reason, we won't be able to do this. This should be fixed. Maybe we should use prefixes? Then the model can be spread to higher-level primitives such as Zeromorph

https://github.com/AztecProtocol/barretenberg/blob/519fb4b40794eddecd686643b5ab62dacbb71d9e/cpp/src/barretenberg/commitment_schemes/kzg/kzg.hpp#L44