Support for executing job and adhoc commands on isolated Tower nodes (#6524)

tools/docker-isolated/README.md

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+## Instructions on using an isolated node
+
+The building of the isolated node is done in the `make docker-compose-build`
+target. Its image uses a different tag from the tools_tower container.
+
+Given that the images are built, you can run the combined docker compose target. This uses
+the base `docker-compose.yml` with modifications found in `docker-isolated-override.yml`.
+You will still need to give COMPOSE_TAG with whatever your intended
+base branch is. For example:
+
+```bash
+make docker-isolated COMPOSE_TAG=devel
+```
+
+This will automatically exchange the keys in order for the `tools_tower_1`
+container to access the `tools_isolated_1` container over ssh.
+After that, it will bring up all the containers like the normal docker-compose
+workflow.
+
+### Running a job on the Isolated Node
+
+Create a job template that runs normally. Add the id of the instance
+group named `thepentagon` to the JT's instance groups. To do this, POST
+the id (probably id=2) to `/api/v2/job_templates/N/instance_groups/`.
+After that, run the job template.
+
+The models are automatically created when running the Makefile target,
+and they are structured as follows:
+
+    +-------+     +-------------+
+    | tower |<----+ thepentagon |
+    +-------+     +-------------+
+        ^                ^
+        |                |
+        |                |
+    +---+---+      +-----+----+
+    | tower |      | isolated |
+    +-------+      +----------+
+
+The `controller` for the group "thepentagon" and all hosts therein is
+determined by a ForeignKey within the instance group.
+
+## Development Testing Notes
+
+### Test the SSH connection between containers
+
+While the environment is running, you can test the connection like so:
+
+```bash
+docker exec -i -t tools_tower_1 /bin/bash
+```
+
+Inside the context of that container:
+
+```bash
+ssh root@isolated
+```
+
+(note: awx user has been deprecated)
+
+This should give a shell to the `tools_isolated_1` container, as the
+`tools_tower_1` container sees it.
+
+### Start the playbook service
+
+The following command would run the playbook for job 57.
+
+```bash
+systemctl start playbook@57.service
+```
+