[#13] chain: Introduce ChainID type

Signed-off-by: aarifullin <aarifullin@yadro.com>

chain.go

@@ -13,7 +13,12 @@ type Engine interface {
 	IsAllowed(name Name, namespace string, r Request) (Status, bool)
 }
 
+// ChainID is the ID of rule chain.
+type ChainID string
+
 type Chain struct {
+	ID ChainID
+
 	Rules []Rule
 }
 

inmemory.go

@@ -1,9 +1,12 @@
 package policyengine
 
+import "sync/atomic"
+
 type inmemory struct {
-	namespace map[Name][]chain
-	resource  map[Name][]chain
-	local     map[Name][]*Chain
+	chainCounter atomic.Uint32
+	namespace    map[Name][]chain
+	resource     map[Name][]chain
+	local        map[Name][]*Chain
 }
 
 type chain struct {