Allow an input filter per HTTP method

- Allows an input filter per HTTP method. If an input filter is defined
  for the selected controller service and the current request method, it
  will be used. Next, if a general input filter (`input_filter` subkey)
  is defined for the controller service, then that will be used.
  Otherwise, no validation will be run.
CS fixes

- trailing whitespace
Merge branch 'feature/http-method-specific-validation'

Allow an input filter per HTTP method for each controller service.