AGC2 adaptive digital controller config: new param

This CL adds and wires up a parameter (namely, adjacent speech
frames threshold) used in `AdaptiveDigitalGainApplier`.

Tested: bit-exactness verified with audioproc_f

Bug: webrtc:7494
Change-Id: I751cd91f08a6e98ee20f767c8df0ed121c8d4b68
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/186049
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32264}
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index 43c40ff..f16f0ad 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -348,6 +348,7 @@
         LevelEstimator level_estimator = kRms;
         bool use_saturation_protector = true;
         float extra_saturation_margin_db = 2.f;
+        int gain_applier_adjacent_speech_frames_threshold = 1;
       } adaptive_digital;
     } gain_controller2;