Command global prefix

[elysrivero99]

Today, @CommandGroup(prefix = "...") lets you namespace commands within a single class, but there is no way to apply a prefix to every command in an application at once. This is useful when embedding a Spring Shell application inside a larger system where all commands need to share a consistent namespace.

This change introduces the spring.shell.command.prefix property as a global prefix. When set, it is prepended to the name of every user-defined @command method. If a @CommandGroup annotation also defines a prefix on the declaring class, both are chained — global prefix first, then group prefix, then the command name. Built-in standard commands (help, clear, version, etc.) are not affected.

Scenario	Resulting command name
Global shell, no group prefix, command hello	shell hello
Global shell, group prefix my-group, command hello	shell my-group hello
No global prefix, group prefix my-group, command hello	my-group hello
No prefixes set	unchanged