Rename standalone to local

[leighmcculloch]

What

Rename the standalone network to local, adding a --local option to enable it, but keep the same network passphrase and keep the old --standalone around for backwards compatibility.

Why

It's very confusing that the standalone network is named standalone, because stellar-core has a standalone mode and the standalone network only sometimes runs in standalone mode.

The name standalone for the network is a carry over from the past. Once-upon-a-time the standalone network always ran stellar-core in standalone mode. Standalone mode causes stellar-core to not interact with any peer, even local peers.

With the invention of captive-core, where horizon and soroban-rpc ingest network data by running their own stellar-core's, standalone mode is largely not useful in the quickstart image. The stellar-core's run by the other services must peer with the main stellar-core validator node in the container, and so it doesn't actually run in standalone mode for the standalone network.

This has been a source of confusion and has almost led to us making technical decisions that would have been incompatible with quickstart because there was an assumption that standalone network always ran in standalone mode.

Local seems like a simple short name that clearly signals that a network is created local to the container.

Keeping the existing standalone option around seems wise for backwards compatibility. A log message is outputted when the --standalone option is used in hope folks will change to --local over time.

[sreuland]

sounds good, the only feedback I can suggest is to consider sandbox rather than local as part of terminology usually associated to development purposes also.