Create .changes files for reproducible builds

release rpm files currently do not have .changes files, but these are
needed to extract SOURCE_DATE_EPOCH for reproducible builds.

Using the time stamp of the last commit to the input, which is the
000package-groups source package, as the time for the changes entry
would be reproducible, however there is resistance to that.

The other date that would is somewhat related is the time of the last
source change for any input to the whole distribution, however AFAIK
this date is not cheap enough to compute for OBS-VCS. This hopefully
changes once we move to git. But I think the change date of
000package-groups makes more sense conceptually, because AFAIK that is
the only information that can causes a change.

However to not delay making progress with reproducible builds in
Factory, I propose this change which is non-reproducible, by using the
current wall-clock time. We can revisit this later.

See https://reproducible-builds.org/ for more general information on
this topic.

pkglistgen/tool.py

@@ -8,6 +8,8 @@
 import subprocess
 import yaml
 
+from datetime import datetime, timezone
+
 from typing import Any, Mapping, Optional
 
 from lxml import etree as ET
@@ -717,6 +719,14 @@ def update_and_solve_target(
         if not product_version:
             # for stagings the product version doesn't matter (I hope)
             product_version = '1'
+        with open(product_dir + "/release.changes", 'w', encoding="utf-8") as f:
+            date = datetime.now(timezone.utc)
+            date = date.strftime("%a %b %d %H:%M:%S %Z %Y")
+            f.write(
+                "-------------------------------------------------------------------\n"
+                + date + " - openSUSE <packaging@lists.opensuse.org>\n\n"
+                "- automatically generated by openSUSE-release-tools/pkglistgen\n\n"
+            )
         for product_file in glob.glob(os.path.join(product_dir, '*.product')):
             self.replace_product_version(product_file, product_version)
             logging.debug(subprocess.check_output(
@@ -730,6 +740,8 @@ def update_and_solve_target(
 
         spec_files = glob.glob(os.path.join(product_dir, '*.spec'))
         file_utils.move_list(spec_files, release_dir)
+        changes_files = glob.glob(os.path.join(product_dir, '*.changes'))
+        file_utils.move_list(changes_files, release_dir)
         inc_files = glob.glob(os.path.join(group_dir, '*.inc'))
         # filter special inc file
         inc_files = filter(lambda file: file.endswith('weakremovers.inc'), inc_files)