fix: Be aware of ForcePrepend

Previously, the value of `ForcePrepend` was not used anywhere and was not behaving as specified.
With this commit, the behavior will be as specified.

Referenced Documents:
- https://github.com/asdf-vm/asdf/blob/932ac468b7c24c2adef90a293a1f7280a0074cc4/docs/manage/configuration.md#asdf_force_prepend

Background:

@andrecloutier told about this issue me in a comment on another PullRequest. Thank you!
- #2011 (comment)

Author: machupicchubeta

Diff for: internal/cli/cli.go

@@ -524,7 +524,7 @@ func envCommand(logger *log.Logger, shimmedCommand string, args []string) error
 		"ASDF_INSTALL_TYPE":    parsedVersion.Type,
 		"ASDF_INSTALL_VERSION": parsedVersion.Value,
 		"ASDF_INSTALL_PATH":    installs.InstallPath(conf, plugin, parsedVersion),
-		"PATH":                 setPath(execPaths),
+		"PATH":                 setPath(conf, execPaths),
 	}
 
 	if parsedVersion.Type != "system" {
@@ -547,8 +547,13 @@ func envCommand(logger *log.Logger, shimmedCommand string, args []string) error
 	return err
 }
 
-func setPath(paths []string) string {
-	return strings.Join(paths, ":") + ":" + os.Getenv("PATH")
+func setPath(conf config.Config, paths []string) string {
+	currentPaths := os.Getenv("PATH")
+
+	if conf.ForcePrepend {
+		return strings.Join(append(paths, currentPaths), ":")
+	}
+	return strings.Join(append([]string{currentPaths}, paths...), ":")
 }
 
 func execCommand(logger *log.Logger, command string, args []string) error {
@@ -583,7 +588,7 @@ func execCommand(logger *log.Logger, command string, args []string) error {
 		"ASDF_INSTALL_TYPE":    parsedVersion.Type,
 		"ASDF_INSTALL_VERSION": parsedVersion.Value,
 		"ASDF_INSTALL_PATH":    installs.InstallPath(conf, plugin, parsedVersion),
-		"PATH":                 setPath(execPaths),
+		"PATH":                 setPath(conf, execPaths),
 	}
 
 	if parsedVersion.Type != "system" {

Diff for: internal/cli/cli_test.go

@@ -0,0 +1,32 @@
+package cli
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/asdf-vm/asdf/internal/config"
+)
+
+func TestSetPath(t *testing.T) {
+	originalPaths := "/dummy/bin:/example/bin"
+	t.Setenv("PATH", originalPaths)
+
+	t.Run("When ForcePrepend turned on", func(t *testing.T) {
+		paths := setPath(
+			config.Config{ForcePrepend: true},
+			[]string{"/awesome/bin", "/cool/bin"},
+		)
+
+		assert.Equal(t, paths, "/awesome/bin:/cool/bin:"+originalPaths, "Then prepend path directories to the front-most part of PATH env")
+	})
+
+	t.Run("When ForcePrepend turned off", func(t *testing.T) {
+		paths := setPath(
+			config.Config{ForcePrepend: false},
+			[]string{"/awesome/bin", "/cool/bin"},
+		)
+
+		assert.Equal(t, paths, originalPaths+":/awesome/bin:/cool/bin", "Then append path directories to the hinder-most part of PATH env")
+	})
+}