soroban-rpc: improve missing command line arguments message

[tsachiherman]

What

Existing reported output in the case of missing command line arguments aren't great:

• it only print out the first missing command line argument.
• it print it out as "invalid config value" ( which is just not true )

Why

The goal is to give the user a complete set of the missing command line arguments, so that the errors could all be resolved at once instead of "tipping" the user for one missing argument at a time.

before:

soroban-rpc
Invalid config value for captive-core-config-path: captive-core-config-path is required. Please specify --captive-core-config-path on the command line or set CAPTIVE_CORE_CONFIG_PATH in the config file.

after:

soroban-rpc
The following required configuration parameters are missing:
*	captive-core-config-path is required. Please specify --captive-core-config-path on the command line or set CAPTIVE_CORE_CONFIG_PATH in the config file.
 	path to additional configuration for the Stellar Core configuration file used by captive core. It must, at least, include enough details to define a quorum set
*	history-archive-urls is required. Please specify --history-archive-urls on the command line or set HISTORY_ARCHIVE_URLS in the config file.
 	comma-separated list of stellar history archives to connect with
*	network-passphrase is required. Please specify --network-passphrase on the command line or set NETWORK_PASSPHRASE in the config file.
 	Network passphrase of the Stellar network transactions should be signed for. Commonly used values are "Test SDF Future Network ; October 2022", "Test SDF Network ; September 2015" and "Public Global Stellar Network ; September 2015"

Known limitations

n/a