feat: Command.SetVersionFunc

Currently, we can use `Command.Version` and `Command.SetVersionTemplate`, which generally works fine.

I would like to propose a `Command.SetVersionFunc`, similar to `command.SetHelpFunc`.

The rationale behind it is that the caller can style the output conditionally, e.g.:

```
$ pgr -v
styled version output

$ pgr -v | cat
plain-text version output (output not a tty)
```

Right now, the way around it is to, before executing the root command, check if output is a terminal, detect color profile, build and set a styled template.

This works, but can interfere with content being piped in/out (e.g. if you want to detect terminal background color and other terminal features).

Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com>

Author: caarlos0

command.go

@@ -190,6 +190,8 @@ type Command struct {
 
 	// versionTemplate is the version template defined by user.
 	versionTemplate *tmplFunc
+	// versionFunc is the version func defined by user.
+	versionFunc func(*Command) error
 
 	// errPrefix is the error message prefix defined by user.
 	errPrefix string
@@ -363,6 +365,14 @@ func (c *Command) SetHelpTemplate(s string) {
 	c.helpTemplate = tmpl(s)
 }
 
+// SetVersionFunc sets version function. Can be defined by Application.
+//
+// Setting this means that [Command.SetVersionTemplate] will not have any
+// effect any more.
+func (c *Command) SetVersionFunc(f func(*Command) error) {
+	c.versionFunc = f
+}
+
 // SetVersionTemplate sets version template to be used. Application can use it to set custom template.
 func (c *Command) SetVersionTemplate(s string) {
 	if s == "" {
@@ -639,6 +649,18 @@ func (c *Command) getVersionTemplateFunc() func(w io.Writer, data interface{}) e
 	return defaultVersionFunc
 }
 
+// getVersionFunc sreturns the version function for the command going up the
+// command tree if necessary.
+func (c *Command) getVersionFunc() func(*Command) error {
+	if c.versionFunc != nil {
+		return c.versionFunc
+	}
+	if c.HasParent() {
+		return c.parent.parent.parent.getVersionFunc()
+	}
+	return nil
+}
+
 // ErrPrefix return error message prefix for the command
 func (c *Command) ErrPrefix() string {
 	if c.errPrefix != "" {
@@ -943,6 +965,9 @@ func (c *Command) execute(a []string) (err error) {
 			return err
 		}
 		if versionVal {
+			if fn := c.getVersionFunc(); fn != nil {
+				return fn(c)
+			}
 			fn := c.getVersionTemplateFunc()
 			err := fn(c.OutOrStdout(), c)
 			if err != nil {