[docs] Add release notes for HD master key -> HD seed rename

Author: jnewbery

doc/release-notes-pr12924.md

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+RPC changes
+------------
+
+### Low-level changes
+
+- The `getwalletinfo` RPC method now returns an `hdseedid` value, which is always the same as the incorrectly-named `hdmasterkeyid` value. `hdmasterkeyid` will be removed in V0.18.
+- The `getaddressinfo` RPC method now returns an `hdseedid` value, which is always the same as the incorrectly-named `hdmasterkeyid` value. `hdmasterkeyid` will be removed in V0.18.
+
+Other API changes
+-----------------
+
+- The `inactivehdmaster` property in the `dumpwallet` output has been corrected to `inactivehdseed`