Plugin settings (#4143)

* Add backend support for plugin settings
* Add plugin settings config
* Add UI support for plugin settings

pkg/plugin/setting.go

@@ -0,0 +1,50 @@
+package plugin
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+)
+
+type PluginSettingTypeEnum string
+
+const (
+	PluginSettingTypeEnumString  PluginSettingTypeEnum = "STRING"
+	PluginSettingTypeEnumNumber  PluginSettingTypeEnum = "NUMBER"
+	PluginSettingTypeEnumBoolean PluginSettingTypeEnum = "BOOLEAN"
+)
+
+var AllPluginSettingTypeEnum = []PluginSettingTypeEnum{
+	PluginSettingTypeEnumString,
+	PluginSettingTypeEnumNumber,
+	PluginSettingTypeEnumBoolean,
+}
+
+func (e PluginSettingTypeEnum) IsValid() bool {
+	switch e {
+	case PluginSettingTypeEnumString, PluginSettingTypeEnumNumber, PluginSettingTypeEnumBoolean:
+		return true
+	}
+	return false
+}
+
+func (e PluginSettingTypeEnum) String() string {
+	return string(e)
+}
+
+func (e *PluginSettingTypeEnum) UnmarshalGQL(v interface{}) error {
+	str, ok := v.(string)
+	if !ok {
+		return fmt.Errorf("enums must be strings")
+	}
+
+	*e = PluginSettingTypeEnum(str)
+	if !e.IsValid() {
+		return fmt.Errorf("%s is not a valid PluginSettingTypeEnum", str)
+	}
+	return nil
+}
+
+func (e PluginSettingTypeEnum) MarshalGQL(w io.Writer) {
+	fmt.Fprint(w, strconv.Quote(e.String()))
+}