This change overhauls the underlying architecture of the submission
client, but it is intended to entirely preserve existing behavior of
Spark applications. Therefore users will find this to be an invisible
change.

The philosophy behind this design is to reconsider the breakdown of the
submission process. It operates off the abstraction of "submission
steps", which are transformation functions that take the previous state
of the driver and return the new state of the driver. The driver's state
includes its Spark configurations and the Kubernetes resources that will
be used to deploy it.

Such a refactor moves away from a features-first API design, which
considers different containers to serve a set of features. The previous
design, for example, had a container files resolver API object that
returned different resolutions of the dependencies added by the user.
However, it was up to the main Client to know how to intelligently
invoke all of those APIs. Therefore the API surface area of the file
resolver became untenably large and it was not intuitive of how it was
to be used or extended.

This design changes the encapsulation layout; every module is now
responsible for changing the driver specification directly. An
orchestrator builds the correct chain of steps and hands it to the
client, which then calls it verbatim. The main client then makes any
final modifications that put the different pieces of the driver
together, particularly to attach the driver container itself to the pod
and to apply the Spark configuration as command-line arguments.

…-spark-on-k8s/spark into submission-steps-refactor

…sionStepSuite

…n-k8s/spark into submission-steps-refactor

Multi-line methods should have four-space indentation for arguments that
aren't on the same line as the method call itself... but this is
difficult to do consistently given how IDEs handle Scala multi-line indentation
in most cases.