feature flags to disable/enable services

[hackaugusto]

we have implemented a node binary, that runs all 3 services (rpc, block_producer, and store) in the same process. this simplifies a lot of things including stdin/stdout/stderr, process management, shutdown, testing.

now that we have a single binary, we can add flags or subcommands to control which services are executed, e.g. miden-node services run, miden-node store run, miden-store rpc run.

This approach simplifies a few things:

• deployment, specially with static linking since a single binary can be copied to multiple machines, and only the process management config need to change to choose which service is executed.
• compilation, since we don't have to compile 3 binaries, but a single one, we should get a small speed up
• testing, since we no longer have to add infrastructure to build and test multiple binaries
• user onboarding, we can do releases of a single binary per platform, and an operator can just download that to do testing

[plafer]

Relating to #100, this means that we only ever need just one config file. If someone wants to run e.g. only the store, then they only need to have the [store] header in their config.

[bobbinth]

Closed by #323.