Move query interceptor to an internal plugin interface (#120308)

Query interceptor is meant for internal modules to implement, not any
external plugin. Yet it is defined on SearchPlugin that is available to
all plugin authors. This commit creates an InternalSearchPlugin
interface and moves the query interceptor method to that.

server/src/main/java/module-info.java

@@ -394,6 +394,7 @@ module org.elasticsearch.server {
     exports org.elasticsearch.action.downsample;
     exports org.elasticsearch.plugins.internal
         to
+            org.elasticsearch.inference,
             org.elasticsearch.metering,
             org.elasticsearch.stateless,
             org.elasticsearch.settings.secure,