Add tx edit.

[fnando]

What

Add tx edit, so users can edit a transaction envelope using JSON in a configured editor (it reads the STELLAR_EDITOR, EDITOR and VISUAL env vars).

tx-edit.mp4

Why

So users can have a more user friendly way of defining transactions.

Known limitations

There's no JSON autocompletion at the moment, but a future PR will add support for JSON schema's $schema in rs-stellar-xdr, which will make autocompletion work out of the box with editors like VSCode.

Support for JSON schema has been added directly to the CLI. Unfortunately, the JSON schema will be reported as invalid because rs-stellar-xdr does not add $schema as a valid key on each element that allowed in the transaction envelope. This is being tracked here: stellar/rs-stellar-xdr#417

[fnando]

Add support for $schema (marked you on the comments). Other than that, I think this is good to go.

[elizabethengelman]

this is looking awesome 👏

[fnando]

@leighmcculloch @Ifropc @elizabethengelman is this good to go?

[Ifropc]

On top of other comments:
I remember we were talking about recovering from user leaving editor with invalid transaction.
Do we still plan to do it in this PR?

I also think panic needs to be fixed before this can be merged

thread 'main' panicked at cmd/soroban-cli/src/commands/tx/edit.rs:171:75:
called `Result::unwrap()` on an `Err` value: Error("trailing characters", line: 2, column: 12)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

(On leaving editor with invalid JSON)