Improve ALSA PCM plugin compatibility on a2dp-sink, hfp-hf and hsp-hs

[borine]

Permit a BlueALSA PCM to be used more like a hw PCM on a2dp-sink, hfp-hf and hsp-hs nodes by making the PCM capture delay value more useful, and by offering a choice of operating modes to suit different application requirements when a PCM exists but the stream does not offer any samples.

Closes #743

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 74.87923% with 52 lines in your changes missing coverage. Please review.

Project coverage is 70.45%. Comparing base (bc3c2b4) to head (8f99300). Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/asound/bluealsa-pcm.c	73.19%	52 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #745      +/-   ##
==========================================
+ Coverage   70.35%   70.45%   +0.10%     
==========================================
  Files         101      101              
  Lines       16585    16749     +164     
  Branches     2603     2634      +31     
==========================================
+ Hits        11668    11801     +133     
- Misses       4799     4832      +33     
+ Partials      118      116       -2     

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[arkq]

Sorry for the veeeryyy long delay with this PR, but I had a lot of real life related chores lately...

Once again, many thanks for your contributions!