Avoid decoding json when proxying over ws

[uvjustin]

This PR avoids decoding from json when proxying to the ws api.

[codecov]

Codecov Report

Merging #321 (40530cf) into master (7738c09) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #321   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines         1669      1672    +3     
=========================================
+ Hits          1669      1672    +3     

Impacted Files	Coverage Δ
custom_components/frigate/ws_api.py	100.00% <ø> (ø)
custom_components/frigate/api.py	100.00% <100.00%> (ø)

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[dermotduffy]

Thanks @uvjustin !