docs: add release notes

doc/release-notes-6267.md

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+Statistics
+-----------
+
+### New Features
+
+- The Statsd client now supports queueing and batching messages, reducing the number of packets and the rate at which
+  they are sent to the Statsd daemon.
+
+- The maximum size of each batch of messages (default, 1KiB) can be adjusted using `-statsbatchsize` (in bytes)
+  and the frequency at which queued messages are sent to the daemon (default, 1 second) can be adjusted using
+  `-statsduration` (in milliseconds)
+  - `-statsduration` has no bearing on `-statsperiod`, which dictates how frequently some stats are _collected_.
+
+### Deprecations
+
+- `-statsenabled` has been deprecated and enablement will now be implied by the presence of `-statshost`. `-statsenabled`
+  will be removed in a future release.
+
+- `-statshostname` has been deprecated and replaced with `-statssuffix` as the latter is better representative of the
+  argument's purpose. They behave identically to each other. `-statshostname` will be removed in a future
+  release.
+
+- `-statsns` has been deprecated and replaced with `-statsprefix` as the latter is better representative of the
+  argument's purpose. `-statsprefix`, unlike `-statsns`, will enforce the usage of a delimiter between the prefix
+  and key. `-statsns` will be removed in a future release.