Update CHANGES and UPGRADE.txt for 20.0.0

CHANGES

UPGRADE.txt

doc/CHANGES-staging/add_mix_option_to_playback.txt

doc/CHANGES-staging/allow_wildcard_certs.txt

doc/CHANGES-staging/ami_wink.txt

doc/CHANGES-staging/app_confbridge_channels.txt

doc/CHANGES-staging/app_confbridge_hear_join.txt

doc/CHANGES-staging/app_dtmfstore.txt

doc/CHANGES-staging/app_mf_maxdigits.txt

doc/CHANGES-staging/app_mf_mf.txt

doc/CHANGES-staging/app_milliwatt.txt

doc/CHANGES-staging/app_morsecode.txt

doc/CHANGES-staging/app_originate_codecs.txt

doc/CHANGES-staging/app_queue.txt

doc/CHANGES-staging/app_queue_DIALEDPEERNUMBER.txt

doc/CHANGES-staging/app_queue_logintime.txt

doc/CHANGES-staging/app_queue_music.txt

doc/CHANGES-staging/app_queue_nordic_language.txt

doc/CHANGES-staging/app_queue_say_thanks.txt

doc/CHANGES-staging/app_queue_stats.txt