feat (batcher_client): set address as an optional parameter

[taturosati]

Proof generator address is now an optional parameter.

To test

1. Start anvil, batcher, aggregator and operator.
2. Run ```
   pushd batcher/client/ ;
   cargo run --
   --proving_system SP1
   --proof test_files/sp1/sp1_fibonacci.proof
   --vm_program test_files/sp1/sp1_fibonacci-elf
   --conn wss://batcher.alignedlayer.com ;
   popd

3. Run ```
pushd batcher/client/ ; \
cargo run -- \
--proving_system SP1 \
--proof test_files/sp1/sp1_fibonacci.proof \
--vm_program test_files/sp1/sp1_fibonacci-elf \
--conn wss://batcher.alignedlayer.com \
--proof_generator_addr 0x976EA74026E726554dB657fA54763abd0C3a0aa9 ;
popd