Add extensible custom logic to the domain check flow

This also fixes up a hook on the domain create flow custom logic to use a single
parameter, which is the general pattern we want to use going forward. It also
establishes a pattern for custom logic being able to add extensions.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139362230

java/google/registry/flows/custom/CustomLogicFactory.java

@@ -35,4 +35,9 @@ public class CustomLogicFactory {
       EppInput eppInput, SessionMetadata sessionMetadata) {
     return new DomainCreateFlowCustomLogic(eppInput, sessionMetadata);
   }
+
+  public DomainCheckFlowCustomLogic forDomainCheckFlow(
+      EppInput eppInput, SessionMetadata sessionMetadata) {
+    return new DomainCheckFlowCustomLogic(eppInput, sessionMetadata);
+  }
 }