Add Knapsack for improving test runtime #3864

Job	Run time
Build and push Docker image	4m 36s
Lint / Lint JS	21s
Lint / Lint ruby	1m 5s
Lint / Lint SCSS	45s
Lint / Lint ERB	39s
Run the RSpec tests / Run rspec (6, 0)	9m 52s
Run the RSpec tests / Run rspec (6, 1)	32m 17s
Run the RSpec tests / Run rspec (6, 2)	9m 51s
Run the RSpec tests / Run end to end scenarios (6, 0)	14m 59s
Run the RSpec tests / Run rspec (6, 3)	8m 35s
Run the RSpec tests / Run end to end scenarios (6, 1)	15m 56s
Run the RSpec tests / Run rspec (6, 4)	8m 49s
Run the RSpec tests / Run end to end scenarios (6, 2)	15m 54s
Run the RSpec tests / Run rspec (6, 5)	8m 24s
Run the RSpec tests / Run end to end scenarios (6, 3)	14m 39s
Run the RSpec tests / Run end to end scenarios (6, 4)	13m 44s
Run the RSpec tests / Run end to end scenarios (6, 5)	16m 1s
Run Brakeman vulnerability scanner / Brakeman Scan	27s
Run Smoke tests	0s
Deploy review	3m 38s
Deploy staging	1s
Permit merge	1s
Deploy production	1s
Deploy sandbox	1s
	3h 0m 36s

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