CreateProject: Provide signed push option on project creation

Also add acceptance test that non-signed push to project that required
signed push is rejected.

Bug: Issue 7750
Change-Id: I28fa94ad08fb7f21e1af37c251e64421d2e443c2
diff --git a/Documentation/rest-api-projects.txt b/Documentation/rest-api-projects.txt
index 1c54a7f..5a5d42b 100644
--- a/Documentation/rest-api-projects.txt
+++ b/Documentation/rest-api-projects.txt
@@ -3187,6 +3187,12 @@
 |`require_change_id`                           |`INHERIT` if not set|
 Whether the usage of Change-Ids is required for the project (`TRUE`,
 `FALSE`, `INHERIT`).
+|`enable_signed_push`                           |`INHERIT` if not set|
+Whether signed push validation is enabled on the project  (`TRUE`,
+`FALSE`, `INHERIT`).
+|`require_signed_push`                          |`INHERIT` if not set|
+Whether signed push validation is required on the project  (`TRUE`,
+`FALSE`, `INHERIT`).
 |`max_object_size_limit`     |optional|
 Max allowed Git object size for this project.
 Common unit suffixes of 'k', 'm', or 'g' are supported.