cmake: add CURL_PATCHSTAMP configuration variable, test in CI

Also:
- INSTALL-CMAKE.md: alpha sort.

Closes #20576

lib/curl_config-cmake.h.in

@@ -330,6 +330,9 @@
 /* BoringSSL version */
 #cmakedefine CURL_BORINGSSL_VERSION ${CURL_BORINGSSL_VERSION}
 
+/* Patch stamp */
+#cmakedefine CURL_PATCHSTAMP ${CURL_PATCHSTAMP}
+
 /* Define to 1 if you have the <ifaddrs.h> header file. */
 #cmakedefine HAVE_IFADDRS_H 1