Add tests and CI (#34)

* Add first version of tests

From https://github.com/Tecnativa/docker-socket-proxy/pull/14

* Expand tests

* Add GH CI

* Apply suggestions

* Apply autopretty template + fix prettier

* Fix isort

* Apply autoprettier

* Fix VSCode settings

* Make tests run in parallel

* Build docker image before testing

* Update workspace settings

* Try multi-platform builds and push to ghcr.io

* Push to docker hub as well from ci

* Upgrade autopretty

* Update pyproject configurations

* Improve test configuration and execution

TT26468

* Provide initial conftest

* Improve tests

* Add python3 in image

* Remove POST rule from proxy

* Build image before testing and push at the end

Builds the image (in single arch) before testing
Loads the image into local docker (See https://github.com/docker/build-push-action#export-image-to-docker

)
Rebuilds and pushes the final image in multi-arch at the end.

* Fix python path

* Remove build fixture from tests to see if image is built in CI

* Organize docker tests definition and document

* Restore fixture allowing usage for local testing

This reverts commit dc0b60e6 and allows using `--prebuild` CLI flag for pytest when doing local tests.

Co-authored-by: Jairo Llopis <jairo.llopis@tecnativa.com>