Implement experimental REST API endpoints for plugins (#7279)

* Implement experimental REST API endpoints for plugins

* Updates per feedback and rebase

* Update tests

* Further updates

* Update extraction of plugins

* Use OS temp dir for plugins instead of search path

* Fail extraction on paths that attempt to traverse upward

* Update pluginenv ActivePlugins()

model/config.go

@@ -477,6 +477,7 @@ type JobSettings struct {
 }
 
 type PluginSettings struct {
+	Enable  *bool
 	Plugins map[string]interface{}
 }
 
@@ -1522,6 +1523,11 @@ func (o *Config) SetDefaults() {
 		*o.JobSettings.RunScheduler = true
 	}
 
+	if o.PluginSettings.Enable == nil {
+		o.PluginSettings.Enable = new(bool)
+		*o.PluginSettings.Enable = false
+	}
+
 	if o.PluginSettings.Plugins == nil {
 		o.PluginSettings.Plugins = make(map[string]interface{})
 	}