CPS-46 Refactor imports

[JaviCerveraIngram]

Put each model in its own Python file, to reduce the chance of having circular references on imports.

[codecov-io]

Codecov Report

Merging #66 into master will increase coverage by 0.75%.
The diff coverage is 99.18%.

@@            Coverage Diff             @@
##           master      #66      +/-   ##
==========================================
+ Coverage   92.05%   92.81%   +0.75%     
==========================================
  Files          32       65      +33     
  Lines        1574     1739     +165     
==========================================
+ Hits         1449     1614     +165     
  Misses        125      125

Impacted Files	Coverage Δ
connect/models/activation_tile_response.py	100% <ø> (ø)
connect/models/product_stats.py	100% <100%> (ø)
connect/models/agreement.py	100% <100%> (ø)
connect/models/param.py	100% <100%> (ø)
connect/models/event.py	100% <100%> (ø)	⬆️
connect/models/product_stats_info.py	100% <100%> (ø)
connect/models/schemas.py	92.64% <100%> (ø)	⬆️
connect/models/customer_ui_settings.py	100% <100%> (ø)
connect/models/configuration.py	100% <100%> (ø)
connect/models/ext_id_hub.py	100% <100%> (ø)
... and 74 more

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