Update ANNOUNCEMENT file

Add remoteauth as a new overlay
Add deprecated backend section and adjust backends accordingly
Mark wired tiger backend as experimental
3 jobs for OPENLDAP_REL_ENG_2_5 in 50 minutes and 3 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build-gnutls-mit-standalone-lloadd #6681

00:45:54

passed build-no-threads-no-slapd #6679

00:02:55

passed build-openssl-heimdal-lloadd #6680

00:50:02