[Draft] Running experiments using latest env in core and flipping curr to latest env in rust bridge

[anupsdf]

What?

Running an experiment to see if core can be build with latest env and curr can point to that in the rust bridge. Doing this experiment only for core-vnext feature.
On limitation is that when latest env is bumped to a new version which hasn't been released, we will see errors like this,

anuppani@Anups-MBP stellar-core % ./src/stellar-core version                                                                                                
thread '<unnamed>' panicked at src/rust/src/lib.rs:594:10:
calculating global dep tree of Cargo.lock: Resolution("failed to find dependency: soroban-env-macros 21.0.0 (git+https://github.com/stellar/rs-soroban-env?branch=main)")
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5
zsh: abort      ./src/stellar-core version

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document