[feature-flag] Add simple feature flag package (#251)

## Summary

Add very simple feature flag package that uses hard coded boolean to switch on and off. Can be overridden on by setting environment variable. 

## How was it tested?

unit tests

Author: mikeland73

boxcli/featureflag/feature.go

@@ -0,0 +1,35 @@
+package featureflag
+
+import (
+	"os"
+	"strconv"
+)
+
+type feature struct {
+	name    string
+	enabled bool
+}
+
+var features = map[string]*feature{}
+
+func disabled(name string) {
+	features[name] = &feature{name: name}
+}
+
+func enabled(name string) {
+	features[name] = &feature{name: name, enabled: true}
+}
+
+func Get(name string) *feature {
+	return features[name]
+}
+
+func (f *feature) Enabled() bool {
+	if f == nil {
+		return false
+	}
+	if on, _ := strconv.ParseBool(os.Getenv("DEVBOX_FEATURE_" + f.name)); on {
+		return true
+	}
+	return f.enabled
+}

boxcli/featureflag/feature_test.go

@@ -0,0 +1,31 @@
+package featureflag
+
+import "testing"
+
+func TestEnabledFeature(t *testing.T) {
+	enabled("TEST")
+	if !Get("TEST").Enabled() {
+		t.Errorf("got Get(%q).Enabled() = false, want true.", "TEST")
+	}
+}
+
+func TestDisabledFeature(t *testing.T) {
+	disabled("TEST")
+	if Get("TEST").Enabled() {
+		t.Errorf("got Get(%q).Enabled() = true, want false.", "TEST")
+	}
+}
+
+func TestEnabledFeatureEnv(t *testing.T) {
+	disabled("TEST")
+	t.Setenv("DEVBOX_FEATURE_TEST", "1")
+	if !Get("TEST").Enabled() {
+		t.Errorf("got Get(%q).Enabled() = false, want true.", "TEST")
+	}
+}
+
+func TestNonExistentFeature(t *testing.T) {
+	if Get("TEST").Enabled() {
+		t.Errorf("got Get(%q).Enabled() = true, want false.", "TEST")
+	}
+}

boxcli/featureflag/pkgconfig.go

@@ -0,0 +1,7 @@
+package featureflag
+
+const PKGConfig = "PKG_CONFIG"
+
+func init() {
+	disabled(PKGConfig)
+}