[#212] Implementation of CHAIN operator in pattern matching query

src/agents/query_engine/query_element/BUILD

@@ -7,6 +7,7 @@ cc_library(
     includes = ["."],
     deps = [
         ":and",
+        ":chain",
         ":iterator",
         ":link_template",
         ":operator",
@@ -44,6 +45,19 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "chain",
+    srcs = ["Chain.cc"],
+    hdrs = ["Chain.h"],
+    deps = [
+        ":operator",
+        "//atomdb:atomdb_singleton",
+        "//commons:commons_lib",
+        "//commons/atoms:atoms_lib",
+        "//commons/processor:processor_lib",
+    ],
+)
+
 cc_library(
     name = "terminal",
     srcs = ["Terminal.cc"],