Rename command registration doc files

Author: jvalkeal

spring-shell-docs/src/main/asciidoc/using-shell-commands-annotationmodel.adoc renamed to spring-shell-docs/src/main/asciidoc/using-shell-commands-registration-legacyannotation.adoc

@@ -7,6 +7,6 @@ in a class and annotate the class and the methods with specific annotations.
 In the programmatic model, you use a more low level approach, defining command
 registrations (either as beans or by dynamically registering with a command catalog).
 
-include::using-shell-commands-annotationmodel.adoc[]
+include::using-shell-commands-registration-legacyannotation.adoc[]
 
-include::using-shell-commands-programmaticmodel.adoc[]
+include::using-shell-commands-registration-programmatic.adoc[]