Add client.wait method

[knkski]

Adds client.wait as a rough analogue of kubectl wait. Builds on top of client.watch to wait for specified resource to enter expected state.

Opening as draft PR to ensure that this is something that is generally desired in lightkube. If so, will also implement logic for AsyncClient and convert to regular PR.

Punts on implementing an equivalent of kubectl wait's --timeout flag, as that would require some deeper changes in how exactly the watch requests are handled. Some extra logic around stream=True and setting the read timeout should work if that's desired, but this PR also includes an example of how to achieve the same thing with gevent.Timeout.

[gtsystem]

I think adding this functionality is a nice idea, as it's not straight forward to implement.

Few things I was thinking about regarding the interface:

• It would be nicer to align the naming more with kubectl, so instead of success_conditions maybe for_conditions.
• In the future we could also add support for "wait for delete" using for_delete=True.
• Failure cases are not supported by kubectl but I think it's a good addition, we could name it raise_for_conditions (this clarify that the effect is an exception and is similar to requests method raise_for_status ).
• Defaults: I'm not sure providing this defaults are a good idea:
  1. Success conditions can vary across different resources and new ones can come in the future, once we define this default DEFAULT_SUCCESS_CONDITIONS we cannot modify it as it would be a breaking change. I would prefer this parameter to be required instead (as in kubectl wait)
  2. Checking for failures may not be always wanted and to disable this default the user will be force to add raise_for_status=[] which is not ideal. Empty should be the default instead.
• kubectl supports passing the condition status to verify (true or false). Not sure how useful this is but we could support this in the future using a dict like value instead for_conditions={"Available": False}.
• timeout: This is something we may want to support but we could go without it for the first version.

Any opinion/idea?

[knkski]

Thanks for the review, and sorry for the slow response. I've updated this branch with all requested changes other than the timeouts and for_conditions supporting a dict-like value. I've also added AsyncClient.wait to mirror Client.wait.

[gtsystem]

Code coverage for the two new functions is missing. Tests should go in tests/test_client.py and tests/test_async_client.py. Be sure we are covering every condition.

[gtsystem]

Merged. @knkski, thanks a lot for the contribution :)