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()

api4/params.go

@@ -24,6 +24,7 @@ type ApiParams struct {
 	ChannelId      string
 	PostId         string
 	FileId         string
+	PluginId       string
 	CommandId      string
 	HookId         string
 	ReportId       string
@@ -78,6 +79,10 @@ func ApiParamsFromRequest(r *http.Request) *ApiParams {
 		params.FileId = val
 	}
 
+	if val, ok := props["plugin_id"]; ok {
+		params.PluginId = val
+	}
+
 	if val, ok := props["command_id"]; ok {
 		params.CommandId = val
 	}