Add System Runtime Caches endpoint bindings

[tdstein]

Add support for the System Runtime Caches API. See https://docs.posit.co/connect/api/#get-/v1/system/caches/runtime

This should be implemented as a new resource and resemble the following pseudo-code:

from posit import connect
from posit.connect.system import System, SystemCache

client = connect.Client()
system: System = client.system
caches: List[SystemCache]: system.caches
for cache in caches:
    task = cache.destroy(dry_run=True)