Add release notes

ci/release_notes.md

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+# New Features
+
+- Syslog length and format can now be configured via `ha_proxy.log_max_length` and `ha_proxy.log_format`.
+  Defaults remain unchanged at 1024 bytes, and rfc3164.
+
+- HAProxy can now bind to the default interface on both IPv4 and IPv6 simultaneously, via the `ha_proxy.v4v6`
+  property. When this is set, you must also set the `ha_proxy.binding_ip` to `::` for it to take effect. This
+  feature is off by default.
+
+
+# Acknowledgements
+
+Thanks go to @cunnie for the IPv6 binding, and @msahihi for the log customization PRs!