update changelog for 9.0

CHANGELOG

@@ -1,3 +1,37 @@
+Version 9.0 - Mar 2nd, 2024
+===========================
+
+- Added support for RPKI Signed Prefix Lists
+
+  Signed Prefix Lists carry he complete list of prefixes which an Autonomous
+  System may originate its routing peers. The validation of a Signed Prefix
+  List confirms that the holder of the listed ASN produced the object. This
+  list is a current, accurate and complete description of address prefixes
+  that may be announced into the routing system originated by this AS.
+
+  https://datatracker.ietf.org/doc/html/draft-ietf-sidrops-rpki-prefixlist
+
+  Signed prefix lists are only parsed in filemode or if rpki-client is run
+  with the new -x flag.
+
+- Added an -x flag to opt into parsing and evaluation of file types that are
+  still considered experimental. At this point in time this covers the signed
+  prefix lists.
+
+- Added a metric to track the number of new files that were moved to the
+  validated cache. In the OpenMetrics output, per-repository counters are
+  shown. The main process and the JSON output only show the total.
+
+- Per the announcement in the last release, the stale manifest counters were
+  removed from the OpenMetrics and the JSON output.
+
+- Ensure that the FileAndHashes list in a Manifest contains no duplicate
+  file names and no duplicate hashes.
+
+- Various refactoring work, notably to reduce the warning spam generated by
+  OpenSSL 3's deprecations and to remove unergonomic internal structs.
+
+
 Version 8.9 - Feb 13th, 2024
 ============================