Fix Rubocop violations

[#65117796]

Signed-off-by: Ruth Byers <rbyers@pivotallabs.com>
Introduce Rubocop

All violations have currently been added as exceptions to rubocop-todo.yml

[#65117796]

Signed-off-by: Ruth Byers <rbyers@pivotallabs.com>
Ignore vendor directory during Rubocop run

[#65117796]

Signed-off-by: Ruth Byers <rbyers@pivotallabs.com>