Add config options for extra security groups and iam policies for hea…

…d and compute nodes (#228)

Add the following config options:
* slurm/ParallelClusterConfig/ClusterConfig
* slurm/SlurmCtl/AdditionalSecurityGroups
* slurm/SlurmCtl/AdditionalIamPolicies
* slurm/SlurmCtl/Imds/Secured
* slurm/InstanceConfig/AdditionalSecurityGroups
* slurm/InstanceConfig/AdditionalIamPolicies

Added documentation for all config parameters.

Changed the StackName default from slurm-top to slurm-config.

Fix the slurm/ParallelClusterConfig/Dcv/Enabled option.
Change the option name from Enable to Enabled to match ParallelCluster.

Fix the setting of ParallelCluster HeadNode/Dcv/AllowedIps config
Was setting from non-existent slurm/ParallelClusterConfig/AllowedIps instead of slurm/ParallelClusterConfig/HeadNode/Dcv/AllowedIps.

Delete the following config option because it uses legacy cluster.
* slurm/EdfaSlurmClusterStackName

Resolves #225