union: enable passing of options to upstreams and policies #6071

This factors out the options into a sub package so they can be passed
to upstreams and used in policies.

backend/union/common/options.go

@@ -0,0 +1,16 @@
+// Package common defines code common to the union and the policies
+//
+// These need to be defined in a separate package to avoid import loops
+package common
+
+import "github.com/rclone/rclone/fs"
+
+// Options defines the configuration for this backend
+type Options struct {
+	Upstreams    fs.SpaceSepList `config:"upstreams"`
+	Remotes      fs.SpaceSepList `config:"remotes"` // Deprecated
+	ActionPolicy string          `config:"action_policy"`
+	CreatePolicy string          `config:"create_policy"`
+	SearchPolicy string          `config:"search_policy"`
+	CacheTime    int             `config:"cache_time"`
+}