feat: tx sign --sign-with-lab

[elizabethengelman]

This branch is based on #1590.

Companion Lab PR: stellar/laboratory#987 (merged)

old pr: #1579

What

Closes #1428

This PR adds the ability to sign a tx via lab, by opening lab in the browser with the xdr prefilled in the Lab UI.

To test, on this branch, run:

• you can generate your tx xdr, but this example uses xdr created from deploying the test_hello_world contract.
  (stellar contract deploy --wasm target/wasm32-unknown-unknown/test-wasms/test_hello_world.wasm --build-only --network testnet --source testnet-alice)
• run the following from the root dir of this project, on this branch:

echo AAAAAgAAAADcOHnq5sGLOngOCEMyLqqn5CvFV2HGbOSjJAIzhqBdkAAAAGQAEb7UAAAAAQAAAAAAAAAAAAAAAQAAAAAAAAAYAAAAAQAAAAAAAAAAAAAAANw4eermwYs6eA4IQzIuqqfkK8VXYcZs5KMkAjOGoF2Q04SY/PMseMCgfbEFkX5gTr9qD/d0mvD9H3acFOz/X5oAAAAALtGgcgsAibk5q8VOLY2R1G1NdGX7fLzlz7iBFBy64JIAAAAAAAAAAAAAAAA= \
| cargo run tx sign --network testnet \
--sign-with-lab \
--lab-url http://laboratory-pr987.previews.kube001.services.stellar-ops.com/transaction/sign

Why

This will allow for another way for users to sign their tx.

Known limitations

• Based on discussions during our weekly check-in, this PR is the first step in implementing this feature. For now, when the user adds the --sign-with-lab flag, the CLI will send the transaction's xdr to lab via a query param, and then will print out the xdr to the stdout.

  In future iterations, we may want to send the signed tx xdr back to the command line, but for now the intention is to have the user either:
  a. send the transaction from lab
  b. manually copy the signed xdr from Lab, and paste it back in the command line to use with the cli

• Instead of having the flag be --sign-with-lab, what if we change it to --sign-externally? This would open us up to allow a user to pass in any URL that accepts xdr and networkPasshrase as query params. 🤔

[leighmcculloch]

I merged main into this PR to update it.

Some comments below.

[Ifropc]

In the future it'd be good to add a TODO with a task number in the code