Provision error logs by service and instance on PaaS Docker

Summary:
Currently, logs are unified into a single log file.

If that eases push to ElasticSearch / OpenSearch,
it doesn't offer a comfortable reading with grep/tail/etc.

The new structure will store log files in:

• /var/log/www/<service>/<instance>-error.log
• /var/log/www/<service>/<instance>-access.log

For a service, for example Phabricator, all the containers
have their web logs in the same place, to ease grep search.

Test Plan: Deploy on Dwellers

Reviewers: DorianWinty, sandrined

Reviewed By: sandrined

Differential Revision: https://devcentral.nasqueron.org/D3632