Slack webhook returner

[cdalvaro]

What does this PR do?

Merge slack_webhook returner from develop branch.

What issues does this PR fix or reference?

More information is available in PR #50879

Tests written?

Yes

Commits signed with GPG?

Yes

[Akm0d]

re-run full proxy

[Akm0d]

re-run full m2crypto

[Akm0d]

re-run full m2crypto

[Akm0d]

re-run full amazon2

[max-arnold]

@cdalvaro The returner crashes for simple functions like test.ping:

sudo salt minion1 test.ping --return slack_webhook

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/salt/minion.py", line 1805, in _thread_return
    minion_instance.returners[returner_str](ret)
  File "/usr/lib/python3/dist-packages/salt/returners/slack_webhook_return.py", line 330, in returner
    report = _generate_report(ret, show_tasks)
  File "/usr/lib/python3/dist-packages/salt/returners/slack_webhook_return.py", line 220, in _generate_report
    returns.items(),
AttributeError: 'bool' object has no attribute 'items'

The reason is that the ret dictionary looks like this:

{'success': True, 'return': True, 'retcode': 0, 'jid': '20200112092012145203', 'fun': 'test.ping', 'fun_args': [], 'id': 'minion1'}

and the returner tries to iterate over True.items(). The return key can contain arbitrary values and data structures.

[max-arnold]

Also, it is not mentioned in the docs: https://docs.saltstack.com/en/master/ref/returners/all/index.html

[cdalvaro]

Thank you for the reporting @max-arnold, I will fix it asap! 🛠

Have you detected more issues related with this returner??

[max-arnold]

@cdalvaro I haven't used it heavily yet, so those two problems is all I was able to find.

Overall, the resulting Slack message looks much nicer than raw json dump from the old slack returner.