change from zdesk to zenpy in ZendeskHook

[RosterIn]

Description
zdesk hasn't been updated in two years.
there is a better maintained package zenpy

The ZendeskHook needs to be refactored to work with the new package.

[xrmx]

Looking at the zenpy code it looks like that every endpoint is wrapped in a class, see https://github.com/facetoe/zenpy/blob/master/zenpy/__init__.py#L97. Can't see a sane way to map the plain path to a class to keep backwards compatibility. Said that we can leverage the BaseApi class in https://github.com/facetoe/zenpy/blob/master/zenpy/lib/api.py to get ratelimit handling for free. Do you have any thoughts?

[RosterIn]

@xrmx Since the old package isn't maintained and can't have new functionality I think this change is required even if breaking change. Also Airflow soon change major version which is great because it will be able to introduce breaking changes.
I think better to hear from the project owners @potiuk @kaxil @mik-laj

[kaxil]

Yes I agree, let's use zenpy since zdesk seems to be abandoned.

[eladkal]

@xrmx do you want to work on this task?

[xrmx]

@eladkal nope

I'll give this a shot!

[mik-laj]

I assigned you to this ticket.