doc: bump breathe requirement to >=4.23.0

Breathe>=4.23.0 brings in basic xrefitem rendering support and fixes
issues parsing anonymous struct/unions. This version also adds a config
knob for showing or hiding enumerator values, so set it to generate
documentation compatible with previous versions.

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>