[FEATURE] Add support for mysql version 8

[psycho0verload]

I thought it might be handy to be able to use mysql 8 for further developments.

I have switched from mysql 5 to 8. Consciously to version 8.0 because in future versions the support of the small detour via

command: --default-authentication-plugin=mysql_native_password

is omitted.

[Flightkick]

Instead of downgrading to mysql_native_password, support for caching_sha2_password may be added by installing the mariadb-connector-c-dev apk package here:

https://github.com/invoiceninja/dockerfiles/blob/4b82f750fcf86012c6125172fcc0a154347d1da6/alpine/5/Dockerfile#L53-L60

[psycho0verload]

Instead of downgrading to mysql_native_password, support for caching_sha2_password may be added by installing the mariadb-connector-c-dev apk package here:

https://github.com/invoiceninja/dockerfiles/blob/4b82f750fcf86012c6125172fcc0a154347d1da6/alpine/5/Dockerfile#L53-L60

Instead of downgrading to mysql_native_password, support for caching_sha2_password may be added by installing the mariadb-connector-c-dev apk package here:

https://github.com/invoiceninja/dockerfiles/blob/4b82f750fcf86012c6125172fcc0a154347d1da6/alpine/5/Dockerfile#L53-L60

Yes you are right about that!