Use sync API in event loop

[jacobtomlinson]

Currently the sync API cannot be used in an asyncio event loop. We have an xfailing test which was added in #40 to demonstrate this.

kr8s/kr8s/tests/test_api.py

Lines 60 to 64 in 6cf29b2

	@pytest.mark.xfail(reason="Cannot run nested event loops", raises=RuntimeError)
	async def test_version_sync_in_async():
	kubernetes = kr8s.api()
	version = kubernetes.version()
	assert "major" in version

This situation will come up a lot in Jupyter as there is always an event loop running but many users may expect to be able to use the sync API and will not consider asyncio at all.

We need to be able to support the sync API (which uses asyncio.run under the hood) in an event loop.

[jacobtomlinson]

I started a conversation about this on Twitter and the main suggestions were:

• Many folks solve this problem with nest-asyncio but the Jupyter devs do not recommend it.
• Jupyter currently creates a new thread and event loop within that to solve this.
• There is also a long term plan to solve this in cpython and a discussion around this that recently happened between Guido van Rossum and Jupyter Devs.

[jacobtomlinson]

Tried nest-asyncio but reverted in #44 as it caused more problems than it solved (see #43). This is likely why Jupyter devs recommended against it.

Reopening to track adding this ability back in either via a solution to #43 or using another method like creating a new thread and loop.

[jacobtomlinson]

I ended up going down the same road as Jupyter and if a loop is already running we start a second loop in a new thread and run coroutines there.