Add new "one-click" genny workload tasks to system_perf.yml

TIG-2041 would make it easier to run genny workloads by adding the following new sys_perf tasks:

• genny_patch_tasks: runs all workloads that have been added or modified locally (based on git history)
• genny_auto_tasks: automatically runs workloads based on the evergreen (bootstrap.yml {{}}vars, etc). A new AutoRun section can be added to workload yaml files describing the criteria that must be met for the workload to autorun
• [genny_specified_tasks: if necessary, allows pme to directly specify which workloads to run from within system_perf.yml]

This ticket is to add these tasks to etc/system_perf.yml and remove the existing genny workload task definitions.