Add possibility to set jgit nfs related config

It may be necessary for users to configure jgit behaviour related to
file handling. This commit makes the following two configurations
available (among others):

- core.trustfolderstat
- core.supportsatomicfilecreation

scm-plugins/scm-git-plugin/src/test/java/sonia/scm/repository/spi/GitConfigContextListenerTest.java

@@ -0,0 +1,21 @@
+package sonia.scm.repository.spi;
+
+import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.util.SystemReader;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class GitConfigContextListenerTest {
+
+  @Test
+  void shouldSetGitConfig() throws IOException, ConfigInvalidException {
+    System.setProperty("scm.git.core.someTestKey", "testValue");
+    new GitConfigContextListener().contextInitialized(null);
+    assertThat(
+      SystemReader.getInstance().getSystemConfig().getString("core", null, "someTestKey")
+    ).isEqualTo("testValue");
+  }
+}