Add sync/task endpoint to list all sync tasks

[rochacbruno]

• Added /sync/tasks/ endpoint
• Serializer includes Worker, Child and Parent tasks info
• Using same accesspolicy of CollectionRemote

Issue: #459

Endpoint results

galaxy_ng on  sync_tasks [$] via  v3.8.5 (galaxy_ng) took 4s
❯ galaxy /api/automation-hub/content/rh-certified/v3/sync/tasks/
HTTP/1.1 200 OK
X-Powered-By: Express
allow: GET, HEAD, OPTIONS
connection: close
content-length: 3111
content-type: application/json
date: Thu, 24 Sep 2020 19:04:21 GMT
server: gunicorn/20.0.4
vary: Accept, Cookie
x-frame-options: SAMEORIGIN

{
    "data": [
        {
            "repository": "rh-certified",
            "task": {
                "child_tasks": [],
                "created_at": "2020-09-23T19:48:40.918537Z",
                "error": {
                    "description": "401, message='Unauthorized', url=URL('https://cloud.redhat.com/api/automation-hub/v3/collections?offset=0&limit=100')",
                    "traceback": "  File \"/venv/lib64/python3.6/site-packages/rq/worker.py\", line 934, in perform_job\n    rv = job.perform()\n  File \"/venv/lib64/python3.6/site-packages/rq/job.py\", line 686, in perform\n    self._result = self._execute()\n  File \"/venv/lib64/python3.6/site-packages/rq/job.py\", line 692, in _execute\n    return self.func(*self.args, **self.kwargs)\n  File \"/venv/lib64/python3.6/site-packages/pulp_ansible/app/tasks/collections.py\", line 81, in sync\n    d_version.create()\n  File \"/venv/lib64/python3.6/site-packages/pulpcore/plugin/stages/declarative_version.py\", line 148, in create\n    loop.run_until_complete(pipeline)\n  File \"/usr/lib64/python3.6/asyncio/base_events.py\", line 484, in run_until_complete\n    return future.result()\n  File \"/venv/lib64/python3.6/site-packages/pulpcore/plugin/stages/api.py\", line 225, in create_pipeline\n    await asyncio.gather(*futures)\n  File \"/venv/lib64/python3.6/site-packages/pulpcore/plugin/stages/api.py\", line 43, in __call__\n    await self.run()\n  File \"/venv/lib64/python3.6/site-packages/pulp_ansible/app/tasks/collections.py\", line 288, in run\n    async for metadata in self._fetch_collections():\n  File \"/venv/lib64/python3.6/site-packages/pulp_ansible/app/tasks/collections.py\", line 354, in _fetch_collections\n    initial_data = parse_metadata(await downloader.run())\n  File \"/venv/lib64/python3.6/site-packages/pulpcore/download/base.py\", line 227, in run\n    return await self._run(extra_data=extra_data)\n  File \"/venv/lib64/python3.6/site-packages/backoff/_async.py\", line 133, in retry\n    ret = await target(*args, **kwargs)\n  File \"/venv/lib64/python3.6/site-packages/pulp_ansible/app/downloaders.py\", line 88, in _run\n    return await super()._run(extra_data=extra_data)\n  File \"/venv/lib64/python3.6/site-packages/backoff/_async.py\", line 133, in retry\n    ret = await target(*args, **kwargs)\n  File \"/venv/lib64/python3.6/site-packages/pulpcore/download/http.py\", line 210, in _run\n    self.raise_for_status(response)\n  File \"/venv/lib64/python3.6/site-packages/pulp_ansible/app/downloaders.py\", line 66, in raise_for_status\n    response.raise_for_status()\n  File \"/venv/lib64/python3.6/site-packages/aiohttp/client_reqrep.py\", line 946, in raise_for_status\n    headers=self.headers)\n"
                },
                "finished_at": "2020-09-23T19:48:42.133145Z",
                "parent_task": null,
                "pk": "01c28d6e-ff23-435b-9f90-263c378ca62f",
                "started_at": "2020-09-23T19:48:41.088785Z",
                "state": "failed",
                "updated_at": "2020-09-23T19:48:42.134071Z",
                "worker": {
                    "last_heartbeat": "2020-09-24T19:04:09.825210Z",
                    "missing": false,
                    "name": "1@a2e32df5e8b2"
                }
            }
        }
    ],
    "links": {
        "first": "/api/automation-hub/content/rh-certified/v3/sync/tasks/?limit=10&offset=0",
        "last": "/api/automation-hub/content/rh-certified/v3/sync/tasks/?limit=10&offset=0",
        "next": null,
        "previous": null
    },
    "meta": {
        "count": 1
    }
}

[rochacbruno]

Replaced by #526