DRAFT: Use rs-stellar-xdr for serializing xdr -> json

[drebelsky]

Draft resolves #5041. Will add notes later, but definitely needs some work

[drebelsky]

Brief notes: Besides not building (in CI—it works for me locally), I'm not sure about the double serialization flow (Cereal XDR to bytes -> rust bytes to XDR to JSON). There's also some oddity with picking the right version of rs-stellar-xdr that I haven't fully sorted through, and I don't love the interface with passing the type as a string. All of the ways I could think of for the interface would probably benefit from some level of codegen (e.g., export an enum from rust, codegen the corresponding types in C++ and the parser in rust (could maybe do in the rs-stellar-xdr repo)), although that feels a little ugly. Given this, I'm leaning toward just making sure we have the cereal_overrides for loading corresponding to our archives. (And then, we could add an offline command and some tests to makes sure the flow doesn't lose data.)