soroban-cli: add 'new' / 'init' command that creates a new project with the boilerplate

[leighmcculloch]

Developers would benefit from having a command they can run in soroban-cli that creates a new project with the dependencies and boilerplate already filled out, ready to go.

As evidenced by this discussion, it is easy to miss the simple things like including #![no_std] in the contract.

If developers have a command to run that creates a basic contract to start with, it'll help them get started without getting bogged down in the boilerplate basics.

The command could follow the behaviors of the cargo new and cargo init commands, although for the sake of reducing the surface area of our CLI, it would be nice if we could go with one or the other.

[elizabethengelman]

• First PR: feat: soroban init command #1156
• I'll plan to add the following in a follow up PR:
  • --frontend-template
  • generate the possible example contracts to be included at runtime (https://github.com/stellar/soroban-tools/pull/1156#discussion_r1443144404https://github.com/stellar/soroban-tools/pull/1156#discussion_r1443144404)
  • update the gix version to most recent
  • add a fuzz test / fuzz setup example
  • add an optional --template flag to allow for users to pass in their own template repo: https://github.com/stellar/soroban-tools/pull/1156/files#r1446402707