DOC: Add release not for quantile interpolation rename

Also updates the old release note to include the info (and generally
tweaks it a bit)

Author: seberg

doc/release/upcoming_changes/19857.improvement.rst

@@ -1,8 +1,13 @@
-Add new linear interpolation methods for ``quantile`` and ``percentile``
-------------------------------------------------------------------------
+Add new methods for ``quantile`` and ``percentile``
+---------------------------------------------------
 
-``quantile`` and ``percentile`` now have 13 linear interpolation methods,
-nine of which can be found in the scientific literature.
-The remaining methods are NumPy specific and are kept for backwards
-compatibility. The default is "inclusive" (method 7), whose behavior is equivalent
-to the former default "linear".
+``quantile`` and ``percentile`` now have have a ``method=``
+keyword argument supporting 13 different methods.
+This replaces the ``interpolation=`` keyword argument.
+
+The methods are now aligned with nine methods which can be
+found in scientific literature and the R language.
+The remaining methods are the previous discontinuous variations
+of the default "linear" one.
+
+Please see the documentation of `numpy.percentile` for more information.