Allow overriding upstream ref (elastic#135113)

For most devs the default of finding the elastic remote and the main
branch of that remote is the right upstream ref. But for tests that
operate on fake or local repositories it's useful to be able to override
the ref. This commit adds a parameter to the transport version resources
allowing to override the ref used to look at upstream.

Author: rjernst

build-tools-internal/src/integTest/groovy/org/elasticsearch/gradle/internal/transport/AbstractTransportVersionFuncTest.groovy

@@ -115,6 +115,9 @@ class AbstractTransportVersionFuncTest extends AbstractGradleFuncTest {
             include ':myserver'
             include ':myplugin'
         """
+        propertiesFile << """
+            org.elasticsearch.transports.upstreamRef=main
+        """
         versionPropertiesFile.text = versionPropertiesFile.text.replace("9.1.0", "9.2.0")
 
         file("myserver/build.gradle") << """

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/TransportVersionResourcesPlugin.java

@@ -49,6 +49,10 @@ public void apply(Project project) {
                 Directory transportResources = project.getLayout().getProjectDirectory().dir("src/main/resources/" + resourceRoot);
                 spec.getParameters().getTransportResourcesDirectory().set(transportResources);
                 spec.getParameters().getRootDirectory().set(project.getLayout().getSettingsDirectory().getAsFile());
+                Object upstreamRef = project.findProperty("org.elasticsearch.transport.upstreamRef");
+                if (upstreamRef != null) {
+                    spec.getParameters().getUpstreamRefOverride().set(upstreamRef.toString());
+                }
             });
 
         var depsHandler = project.getDependencies();

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/TransportVersionResourcesService.java

@@ -12,8 +12,10 @@
 import org.gradle.api.file.DirectoryProperty;
 import org.gradle.api.logging.Logger;
 import org.gradle.api.logging.Logging;
+import org.gradle.api.provider.Property;
 import org.gradle.api.services.BuildService;
 import org.gradle.api.services.BuildServiceParameters;
+import org.gradle.api.tasks.Optional;
 import org.gradle.process.ExecOperations;
 import org.gradle.process.ExecResult;
 
@@ -59,6 +61,9 @@ public interface Parameters extends BuildServiceParameters {
         DirectoryProperty getTransportResourcesDirectory();
 
         DirectoryProperty getRootDirectory();
+
+        @Optional
+        Property<String> getUpstreamRefOverride();
     }
 
     @Inject
@@ -79,6 +84,9 @@ public interface Parameters extends BuildServiceParameters {
     public TransportVersionResourcesService(Parameters params) {
         this.transportResourcesDir = params.getTransportResourcesDirectory().get().getAsFile().toPath();
         this.rootDir = params.getRootDirectory().get().getAsFile().toPath();
+        if (params.getUpstreamRefOverride().isPresent()) {
+            upstreamRefName.set(params.getUpstreamRefOverride().get());
+        }
     }
 
     /**