[MRG] Add support for Storage Management

[scaramallion]

Reference issue

Adds support for Storage Management service class, closes #880

Tasks

• Unit tests added that reproduce issue or prove feature is working
• Fix or feature added
• Documentation and examples updated (if relevant)
• Unit tests passing and coverage at 100% after adding fix/feature
• Type annotations updated and passing with mypy

[codecov]

Codecov Report

Merging #889 (0b6a5ba) into main (d38eb18) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #889   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           28        28           
  Lines         8679      8690   +11     
=========================================
+ Hits          8679      8690   +11     

Files	Coverage Δ
pynetdicom/association.py	100.00% <ø> (ø)
pynetdicom/events.py	100.00% <ø> (ø)
pynetdicom/service_class.py	100.00% <100.00%> (ø)
pynetdicom/service_class_n.py	100.00% <100.00%> (ø)
pynetdicom/sop_class.py	100.00% <100.00%> (ø)
pynetdicom/status.py	100.00% <100.00%> (ø)