Add OnFinalize method (#1788)

This method is the OnInitialize counterpart. Like OnInitialize which allows
loading the configuration before each command is executed, OnFinalize allows
saving the configuration after each command has been executed.

command.go

@@ -834,6 +834,8 @@ func (c *Command) execute(a []string) (err error) {
 
 	c.preRun()
 
+	defer c.postRun()
+
 	argWoFlags := c.Flags().Args()
 	if c.DisableFlagParsing {
 		argWoFlags = a
@@ -904,6 +906,12 @@ func (c *Command) preRun() {
 	}
 }
 
+func (c *Command) postRun() {
+	for _, x := range finalizers {
+		x()
+	}
+}
+
 // ExecuteContext is the same as Execute(), but sets the ctx on the command.
 // Retrieve ctx by calling cmd.Context() inside your *Run lifecycle or ValidArgs
 // functions.