DOC: config: add missing glitch_{cnt,rate} sample definitions

DOC: config: add missing glitch_{cnt,rate} sample definitions

Following previous commit, when glitch_cnt and glitch_rate data types were
implemented in c9c6b683f ("MEDIUM: stick-tables: add a new stored type for
glitch_cnt and glitch_rate"), newly exposed samples such as
table_glitch_cnt(), table_glitch_rate, src_glitch_cnt() and
src_glitch_rate() were documented but their definitions was missing in
supported keywords list.

It should be backported in 3.0 with c9c6b683f