Feature/single node check

[rfhaque]

Description

This PR adds a check for the single node experiment
- The single_node variant [default=True] ONLY asserts that the given experiment must run on 1 node
- This check is enforced in the determine_allocation method of the allocation modifier. If single node is enabled and the experiment requires/requests more than 1 node, the ramble setup throws an error
- strong/weak scaling modes are decoupled from the single node mode (it's possible to scale on a single node)
- An experiment trying to run on more than one node must explicitly specify ~single_node

Take 2:

• We add an integer variant max_node_limit to the system specs (lib/benchpark/system.py) which is the max number of nodes allowed for an experiment on that system instantiation. Default value 1, value of 0 means no limits
• In the experiment setup (lib/benchpark/experiment.py), we add a filter clause '{n_nodes} > 0 and {n_nodes} <= {max_node_limit}'.
• The exclude clause filters all experiments that require more than max_node_limit nodes during ramble setup. Currently, it's not an error if zero experiments satisfy the max_node_limit

./bin/benchpark system init --dest=tioga llnl-elcapitan rocm=5.5.1 compiler=cce max_node_limit=1
./bin/benchpark experiment init --dest ./saxpy saxpy +openmp~cuda~rocm caliper=mpi,time
./bin/benchpark setup ./saxpy ./tioga workspace/

Dependencies: FIXME:Add a list of any dependencies.

(Potentially) Fixes #492

Type of Change

• { } Adding a system, benchmark, or experiment
• { } Modifying an existing system, benchmark, or experiment
• { } Documentation update
• { } Build/CI update
• { } Benchpark core functionality

Checklist:

If adding/modifying a system:

• { } Create a new directory for the system and a new system.py file
• { } Add a new dry run unit test in .github/workflows
• { } System appears in System Specifications table in docs catalogue section

If adding/modifying a benchpark:

• { } Add a new application.py and (maybe) package.py under a new directory
  for this benchmark
• { } Configure an experiment
• { } Benchmark appears in Benchmarks and Experiments table in docs catalogue
  section

If adding/modifying a experiment:

• { } Extend experiment.py under existing directory for specific benchmark
• { } Define a single node and multi-node experiments

If adding/modifying core functionality:

• { } Update docs
• { } Update .github/workflows and .gitlab/ci unit tests (if needed)

[pearce8]

@rfhaque what is the status of this PR? How does it currently work? What docs would you need to add?

When you want to run strong or weak scaling, do you need to explicitly disable the single-node test because only one variant is possible at a time? If that is the case, we need to document it well.