refactor: adder interface, rename data client

[acpana]

Following up on punted work items from: #2852

• simplifies the Injector interface for controllers; many controllers don't implement the interface funcs
• renames references to (data) client

[codecov-commenter]

Codecov Report

Patch coverage: 42.30% and project coverage change: +0.10% 🎉

Comparison is base (e138b24) 52.48% compared to head (d58bb22) 52.58%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2991      +/-   ##
==========================================
+ Coverage   52.48%   52.58%   +0.10%     
==========================================
  Files         134      134              
  Lines       11913    11891      -22     
==========================================
+ Hits         6252     6253       +1     
+ Misses       5170     5148      -22     
+ Partials      491      490       -1     

Flag	Coverage Δ
unittests	52.58% <42.30%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
pkg/controller/config/config_controller.go	60.37% <ø> (+2.71%)	⬆️
pkg/controller/constraint/constraint_controller.go	5.72% <0.00%> (+0.03%)	⬆️
...platestatus/constrainttemplatestatus_controller.go	70.58% <ø> (ø)
pkg/controller/expansion/expansion_controller.go	53.52% <ø> (+1.23%)	⬆️
pkg/controller/pubsub/pubsub_config_controller.go	12.50% <ø> (+0.81%)	⬆️
...controller/externaldata/externaldata_controller.go	60.00% <40.00%> (+2.46%)	⬆️
...onstrainttemplate/constrainttemplate_controller.go	61.05% <69.23%> (+1.39%)	⬆️

... and 1 file with indirect coverage changes

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[maxsmythe]

LGTM

[acpana]

@ritazh / @sozercan PTAL 🙏🏼

[sozercan]

Thank you! LGTM