Add support for asyncio

[rlegonidec]

This pull request adds the asyncio support to the lib to close #616 and #1003.

I recently took over my work started in 2021 to add asyncio support. I adapted my original version to handle the changes made since 2021, in particular those related to multi endpoint.

Unlike #1177 or #633 I dont use another gRPC lib to handle asyncio requests. I use the grpcio, this allows me to have the same interface to reuse main code. The port is not finished, there are still to do : locks, alarms and the failover.

I have re-implemented all the request's tests.

The way to use the asyncio version is very similar to the classic version :

import etcd3

etcd = await etcd3.aioclient()

foo = await etcd.get('/foo')
await etcd.put('bar', 'doot')
await etcd.delete('bar')

events_iterator, cancel = await etcd.watch("/doot/watch")
async for event in events_iterator:
    print(event)

TODO

• [x] get methods
• [x] put methods
• [x] replace methods
• [x] delete methods
• [x] watch methods
• [x] transactions
• [x] lease methods
• [x] members methods
• [x] compact
• [x] Finalize merge with the MultiEndpointEtcd3Client (some coroutine was never awaited)
• [x] status
• [x] lock methods
• [x] alarm methods
• [x] defragment
• [x] snapshot
• [x] hash
• [x] failover tests
• [x] Remaining tests

Details

• For now the Etcd3AioClient inherits from the classic MultiEndpointEtcd3Client. Do I keep that or do i implement a common abstract class ?
• I don't support Python 3.6. This version is no longer active. But I could support it if it is a prerequisite with some adaptations. I tested on python 3.7, 3.8, 3.9, 3.10 (need to update dependencies), 3.11 (need to update dependencies)
• I implemented a Github Action to start tests. With the current test dependencies, tests doesn't run for ETCD v3.4+

Tests report

https://github.com/rlegonidec/python-etcd3/actions/runs/5738790855

[SamuelMarks]

@rlegonidec This isn't my project; but I like what you're doing here; maybe you can release something to PyPi?

As it doesn't look like @kragniz is maintaining things anymore 😞