Add privateByDefault config to /config/server/info

Exposing 'privateByDefault' there would be supper useful for polygerrit
when we are implementing the create change dialog.

Change-Id: I248210124a2d972934a94c42c32ccae39c0cfca3

Documentation/rest-api-config.txt

@@ -1473,6 +1473,9 @@ allowed].
 |`large_change`       ||
 link:config-gerrit.html#change.largeChange[Number of changed lines from
 which on a change is considered as a large change].
+|`private_by_default` |not set if `false`|
+Returns true if changes are by default created as private.
+See link:config-gerrit.html#change.privateByDefault[privateByDefault]
 |`reply_label`        ||
 link:config-gerrit.html#change.replyTooltip[Label name for the reply
 button].

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/config/ServerInfoIT.java

@@ -52,6 +52,7 @@ public class ServerInfoIT extends AbstractDaemonTest {
   // change
   @GerritConfig(name = "change.allowDrafts", value = "false")
   @GerritConfig(name = "change.largeChange", value = "300")
+  @GerritConfig(name = "change.privateByDefault", value = "true")
   @GerritConfig(name = "change.replyTooltip", value = "Publish votes and draft comments")
   @GerritConfig(name = "change.replyLabel", value = "Vote")
   @GerritConfig(name = "change.updateDelay", value = "50s")
@@ -93,6 +94,7 @@ public class ServerInfoIT extends AbstractDaemonTest {
     // change
     assertThat(i.change.allowDrafts).isNull();
     assertThat(i.change.largeChange).isEqualTo(300);
+    assertThat(i.change.privateByDefault).isTrue();
     assertThat(i.change.replyTooltip).startsWith("Publish votes and draft comments");
     assertThat(i.change.replyLabel).isEqualTo("Vote\u2026");
     assertThat(i.change.updateDelay).isEqualTo(50);

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/common/ChangeConfigInfo.java

@@ -19,6 +19,7 @@ public class ChangeConfigInfo {
   public Boolean showAssigneeInChangesTable;
   public Boolean allowDrafts;
   public int largeChange;
+  public Boolean privateByDefault;
   public String replyLabel;
   public String replyTooltip;
   public int updateDelay;

gerrit-server/src/main/java/com/google/gerrit/server/config/GetServerInfo.java

@@ -217,6 +217,7 @@ public class GetServerInfo implements RestReadView<ConfigResource> {
         toBoolean(
             cfg.getBoolean("change", "showAssigneeInChangesTable", false) && hasAssigneeInIndex);
     info.largeChange = cfg.getInt("change", "largeChange", 500);
+    info.privateByDefault = toBoolean(cfg.getBoolean("change", "privateByDefault", false));
     info.replyTooltip =
         Optional.ofNullable(cfg.getString("change", null, "replyTooltip")).orElse("Reply and score")
             + " (Shortcut: a)";