Protocol for objects which add a job configuration step.
(apply! job step)
Apply configuration `step` to Hadoop `job`, returning the mutated job. The
`step` may be a function, which will be passed the `job`; a map of configuration
parameters and values; a vector of other steps; or anything implementing the
Base configuration step for job named `jname`.
Base configuration step.
Map of job configuration keys and values implemented by `step`.