Use is_amount clap validator (#7400)

* Fix up is_amount to handle floats for SOL; expand amount_of test

* Use required_lamports_from and is_amount across CLI

* Remove obsolete test (now handled by clap)

cli/src/cluster_query.rs

@@ -127,6 +127,7 @@ impl ClusterQuerySubCommands for App<'_, '_> {
                         .value_name("NUMBER")
                         .takes_value(true)
                         .default_value("1")
+                        .validator(is_amount)
                         .help("Number of lamports to transfer for each transaction"),
                 )
                 .arg(