Webserver: Database listening task does not reconnect when postgres restarts

[sanderegg]

if postgres restarts for any reason, the task listening to notifications of postgres in the webserver does not re-connect with the new instance.
It is locked in

await conn.connection.notifies.get()

osparc-simcore/services/web/server/src/simcore_service_webserver/computation_comp_tasks_listening_task.py

Line 100 in 21c9504

notification = await conn.connection.notifies.get()

see for reference the issue in aiopg which is not resolved

[sanderegg]

when this PR in aiopg goes in aio-libs/aiopg#559
we need to update our codebase and we should be able to cope

[sanderegg]

part of #2212