Throw exceptions for bad input parameters

[slabasan]

Basic exception handling, will work towards creating benchpark-specific exception handling in the future.

Fixes #35

$ benchpark setup sax/cu cts1 .
Traceback (most recent call last):
  ...
ValueError: Invalid benchmark/experiment "sax/cu" - must choose one of:
	saxpy/cuda
	saxpy/rocm
	saxpy/openmp
	amg2023/cuda
	amg2023/rocm
	amg2023/openmp
	raja-perf/cuda
	raja-perf/mpi-only
	raja-perf/rocm
	raja-perf/openmp

$ benchpark list mysys
Traceback (most recent call last):
  ...
ValueError: Invalid benchpark list "mysys" - must choose [benchmarks],[systems], or leave empty

$ benchpark setup saxpy/openmp mysys .
Traceback (most recent call last):
  ...
ValueError: Invalid system "mysys" - must choose one of: 
	cts1
	ats2
	ats4
	x86

$ benchpark se
usage: benchpark [-h] {list,setup} ...
benchpark: error: argument subcommand: invalid choice: 'se' (choose from 'list', 'setup')

$ benchpark setup
usage: benchpark setup [-h] benchmark system workspace_root
benchpark setup: error: the following arguments are required: benchmark, system, workspace_root

$ benchpark --help
usage: benchpark [-h] {list,setup} ...

Benchpark

options:
  -h, --help    show this help message and exit

Subcommands:
  {list,setup}
    list        List available benchmarks and systems
    setup       Create a benchmark and prepare it to build/run