Refactor participants controller

[aanand-1706]

From PR: #192

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	1 Warning
⚠️	Pull request is too big (more than 500 LoC).

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🚨 RSpec Tests Report

All tests passed.

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🚨 RSpec Tests Report

Failing Controller Test Cases:
rspec ./spec/requests/api/v1/participants_controller_spec.rb:56 # Participants API /participants/user/{user_id} get Returns participants returns a 200 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:69 # Participants API /participants/user/{user_id} get Participant not found with user_id returns a 200 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:79 # Participants API /participants/user/{user_id} get User Not Found returns a 404 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:87 # Participants API /participants/user/{user_id} get Unauthorized returns a 401 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:105 # Participants API /participants/assignment/{assignment_id} get Returns participants returns a 200 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:118 # Participants API /participants/assignment/{assignment_id} get Assignment Not Found returns a 404 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:127 # Participants API /participants/assignment/{assignment_id} get Unauthorized returns a 401 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:307 # Participants API /participants/{authorization} post Participant successfully added returns a 201 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:319 # Participants API /participants/{authorization} post Participant successfully added with mixed-case authorization returns a 201 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:342 # Participants API /participants/{authorization} post Participant already exist returns a 500 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:352 # Participants API /participants/{authorization} post User not found returns a 404 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:361 # Participants API /participants/{authorization} post Assignment not found returns a 404 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:370 # Participants API /participants/{authorization} post Authorization not found returns a 422 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:379 # Participants API /participants/{authorization} post Invalid authorization returns a 422 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:389 # Participants API /participants/{authorization} post Test ID 24: Missing user_id in request body returns a 404 response
rspec ./spec/requests/api/v1/participants_controller_spec.rb:400 # Participants API /participants/{authorization} post Test ID 25: Missing assignment_id in request body returns a 404 response

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🚨 RSpec Tests Report

All tests passed.