introduce a new global flag for denoating K8S-based deployments

- In K8S-based installs, only container groups are intended to be used
  for playbook execution (JTs, adhoc, inventory updates), so in this
  scenario, other job types have a task impact of zero.
- In K8S-based installs, traditional instances have *zero* capacity
  (because they're only members of the control plane where services
  - http/s, local control plane execution - run)
- This commit also includes some changes that allow for the task manager
  to launch tasks with task_impact=0 on instances that have capacity=0
  (previously, an instance with zero capacity would never be selected
  as the "execution node"

This means that when IS_K8S=True, any Job Template associated with an
Instance Group will never actually go from pending -> running (because
there's no capacity - all playbooks must run through Container Groups).
For an improved ux, our intention is to introduce logic into the
operator install process such that the *default* group that's created at
install time is a *Container Group* that's configured to point at the
K8S cluster where awx itself is deployed.

awx/settings/defaults.py

@@ -59,6 +59,13 @@ DATABASES = {
     }
 }
 
+# Whether or not the deployment is a K8S-based deployment
+# In K8S-based deployments, instances have zero capacity - all playbook
+# automation is intended to flow through defined Container Groups that
+# interface with some (or some set of) K8S api (which may or may not include
+# the K8S cluster where awx itself is running)
+IS_K8S = False
+
 # TODO: remove this setting in favor of a default execution environment
 AWX_EXECUTION_ENVIRONMENT_DEFAULT_IMAGE = 'quay.io/ansible/awx-ee'