test: add option for keep the test container

[pbalogh-sa]

This can be useful for debugging and checking logs

example usage:

cd integrations
task kind:create
task test:env:gateway:deploy
task test:gateway REMOVE_CONTAINERS=false

docker ps -a
CONTAINER ID   IMAGE                                             COMMAND                  CREATED          STATUS                      PORTS                       NAMES
fad3fddf8e0f   ghcr.io/agntcy/csit/test-langchain-agent:v0.0.1   "poetry run python l…"   23 seconds ago   Exited (0) 15 seconds ago                               reverent_galileo
4a98dd9c08ce   kindest/node:v1.32.0                              "/usr/local/bin/entr…"   19 hours ago     Up 19 hours                 127.0.0.1:65285->6443/tcp   agntcy-test-control-plane

docker logs fad3fddf8e0f

[muscariello]

LGTM