upgrade Percona server to 8.0

[normance]

ISSUE TYPE

Propose Percona Server for MySQL 8.0.13-4

SUMMARY

Max current version in .env is percona-5.7. But the 8.0 exists here https://hub.docker.com/r/percona/percona-server/tags/ (8.0.13 had been released on January 17th, 2019

Goal

Use an mysql alternative with Percona tools

[cytopia]

It is currently under development.

[cytopia]

This has been merged. You should switch to the release branch: #416

Pay attention to how to use it in the PR comment.