doc: samples: Adopt code-sample-category across tree

This commit uses the new .. zephyr:code-sample-category directive to
categorize code samples across the tree.
Updates existing legacy references to manually defined targets to now
use :zephyr:code-sample-category: role instead.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

samples/bluetooth/broadcaster/README.rst

diff --git a/samples/bluetooth/broadcaster/README.rst b/samples/bluetooth/broadcaster/README.rst
index 72e395d..60b4795 100644
--- a/samples/bluetooth/broadcaster/README.rst
+++ b/samples/bluetooth/broadcaster/README.rst
@@ -25,4 +25,4 @@
 This sample can be found under :zephyr_file:`samples/bluetooth/broadcaster` in the
 Zephyr tree.
 
-See :ref:`bluetooth samples section <bluetooth-samples>` for details.
+See :zephyr:code-sample-category:`bluetooth` samples for details.