Feature request: Allow using file-based certificates for front end SSL connections

[pythian-ciciliani]

As discussed with @renecannao , version 2.0 generates SSL certificates for front-end connections (client -> Proxy) at startup and they are kept in memory. We would need ProxySQL to use custom certificates on files.

[renecannao]

Files are all located in datadir:

• proxysql-key.pem
• proxysql-ca.pem
• proxysql-cert.pem

If all 3 files exist, ProxySQL will load them.
If none of the 3 files, ProxySQL will create them.
If only some of the 3 files are present, ProxySQL will refuse to start.

[renecannao]

This is fully implemented.
It only needs to be documented.