Change QueueInterface::getChannel() result type to string only

[vjik]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	✔️

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.09%. Comparing base (4561dde) to head (7f19a30).
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #239      +/-   ##
============================================
+ Coverage     92.87%   93.09%   +0.21%     
  Complexity      359      359              
============================================
  Files            47       47              
  Lines           969      970       +1     
============================================
+ Hits            900      903       +3     
+ Misses           69       67       -2     

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[viktorprogger]

@vjik What's the purpose of channels without adapters? Before this change a channel is a configured adapter.

[vjik]

@vjik What's the purpose of channels without adapters? Before this change a channel is a configured adapter.

Before this change queue also could be without adapter. See code in master branch.