Extract `scan_waku_fleet.py` to a separate container, run as part of waku fleet compose

[igor-sirotin]

Description

Currently we run tests-functional/scripts/scan_waku_fleet.py script as part of the Docker image entrypoint:

status-go/_assets/scripts/entrypoint.sh

Lines 3 to 8 in c575471

	# Define $SCAN_WAKU_FLEET to run a command before running the actual app (CMD).
	# This is expected to be used in functional tests to run `scan_waku_fleet.py` script before starting the app.
	$SCAN_WAKU_FLEET
	# This will exec the CMD from your Dockerfile, i.e. "npm start"
	exec "$@"

This is quite a confusing implementation and:

• unnecessarily pollutes the Dockerfile
• unnecessarily runs the script in each new container

Proposal

The fleet scanning should be extracted into a separate docker image to be executed as part of docker-compose.waku.yml. Then scanning result should then be copied as file from the container (or even be fetched with some API).