feat: soroban init command

[elizabethengelman]

What

This PR adds a soroban init command to the CLI to allow for initializing a new soroban rust project.

Addresses #656

Why

The intention of this change is to make it easier to get up and running with a soroban project, and to allow for the Getting Started guide to be more concise by being able to remove some of the boilerplate Rust setup.

Known limitations

• Currently, this command creates a plain Rust project, there are plans to have a follow-up PR that will allow a user to pass in a specific frontend (--frontend-template) to use so that the project can be set up for frontend development as well. The first FE will be Astro, since we already have an example Astro project working.
• I am seeing a pre-push check failing locally for this branch as well as on main.

error[E0046]: not all trait items implemented, missing: `escalate_error_to_panic`
    --> /Users/elizabethengelman/.cargo/git/checkouts/rs-soroban-sdk-0ab58a716c671239/93b09e4/soroban-sdk/src/env.rs:1449:1
     |
1449 | impl internal::EnvBase for Env {
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `escalate_error_to_panic` in implementation
     |
     = help: implement the missing item: `fn escalate_error_to_panic(&self, _: <Self as soroban_env_host::EnvBase>::Error) -> ! { todo!() }`

[stellarsaur]

Nice addition to the CLI!

[leighmcculloch]

👏🏻 This is looking nice. I tried it out locally and left some comments inline.

[elizabethengelman]

I just pushed up a change that adds the template code in this repo with the increment example contract, which I hope addresses a couple of the outstanding pieces on this PR. d71493f and 4daf40b

• users should be able to run soroban contract init without the need for an internet connection since the template code is in this repo
• the project will include an example contract by default, so that we're not initializing an empty project
• I'm thinking that we can make the inclusion of other examples via --with-example from the examples repo be dependent on an internet connection, and in a follow-up PR we can generate the list instead of hardcoding it, and fall back to just including increment

Right now I just added the template code in cmd/soroban-cli/src/utils/, but in the future, maybe we can think about including it via git submodule or something. But I think that can be an add-on later. Also, happy to rethink if utils is the best place for it.

@leighmcculloch @stellarsaur curious to see what you think!

[chadoh]

Noticed two things that I hope are quick to fix!