Request to add generate-bls-to-execution-change

[0xdcota]

I am sure this must be a work in progress, however, I do not see any open pull request or pretended work to add the
generate-bls-to-execution-change function to this.

If the original ethereum deposit-cli can be used. Please explain if this changes the generated signature values or if only the network name changes when creating the bls_execution_change.json file.

For reference, this is required to update the withdrawal address of validators set some-time ago.