Add parallel processing to the commit validation call

• Add parallel processing to the commit validation call

To improve performance, the processing of commits was moved to be done in parallel through a thread pool. This would allow multiple commits in a request to be processed simultaneously.

src/main/java/org/eclipsefoundation/git/eca/api/models/GithubCommit.java

@@ -106,6 +106,7 @@ public abstract class GithubCommit {
     @AutoValue
     @JsonDeserialize(builder = AutoValue_GithubCommit_GithubCommitUser.Builder.class)
     public abstract static class GithubCommitUser {
+        @Nullable
         public abstract String getLogin();
 
         public static Builder builder() {
@@ -115,7 +116,7 @@ public abstract class GithubCommit {
         @AutoValue.Builder
         @JsonPOJOBuilder(withPrefix = "set")
         public abstract static class Builder {
-            public abstract Builder setLogin(String login);
+            public abstract Builder setLogin(@Nullable String login);
 
             public abstract GithubCommitUser build();
         }