Explicitly include <vector> in cache filter

The filter relied on the session.h including.

server/modules/filter/cache/cache.hh

@@ -16,6 +16,7 @@
 #include <functional>
 #include <memory>
 #include <string>
+#include <vector>
 #include <maxscale/buffer.h>
 #include <maxscale/session.h>
 #include "cachefilter.h"

server/modules/filter/cache/rules.cc

@@ -17,6 +17,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <new>
+#include <vector>
 
 #include <maxscale/alloc.h>
 #include <maxscale/config.h>

server/modules/filter/cache/rules.h

@@ -18,6 +18,7 @@
 #include <stdbool.h>
 #include <jansson.h>
 #include <memory>
+#include <vector>
 #include <maxscale/buffer.h>
 #include <maxscale/session.h>
 #include <maxscale/pcre2.h>