Add release notes

doc/release-notes-24098.md

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+Notable changes
+===============
+
+Updated REST APIs
+-----------------
+
+- The `/headers/` and `/blockfilterheaders/` endpoints have been updated to use
+  a query parameter instead of path parameter to specify the result count. The
+  count parameter is now optional, and defaults to 5 for both endpoints. The old
+  endpoints are still functional, and have no documented behaviour change.
+
+  For `/headers`, use
+  `GET /rest/headers/<BLOCK-HASH>.<bin|hex|json>?count=<COUNT=5>`
+  instead of
+  `GET /rest/headers/<COUNT>/<BLOCK-HASH>.<bin|hex|json>` (deprecated)
+
+  For `/blockfilterheaders/`, use
+  `GET /rest/blockfilterheaders/<FILTERTYPE>/<BLOCK-HASH>.<bin|hex|json>?count=<COUNT=5>`
+  instead of
+  `GET /rest/blockfilterheaders/<FILTERTYPE>/<COUNT>/<BLOCK-HASH>.<bin|hex|json>` (deprecated)
+
+  (#24098)