[lldb/Commands] Align process launch --plugin with process attach (NFC)

Following `7169d3a315f4cdc19c4ab6b8f20c6f91b46ba9b8`, this patch updates
the short option for the plugin command option to (`-p` to `-P`) to
align with the `process attach` command options.

The long option remains the same since there are already the same for both
commands.

Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>

lldb/source/Commands/CommandOptionsProcessLaunch.cpp

@@ -61,7 +61,7 @@ Status CommandOptionsProcessLaunch::SetOptionValue(
     break;
   }
 
-  case 'p': // Process plug-in name
+  case 'P': // Process plug-in name
     launch_info.SetProcessPluginName(option_arg);
     break;