Mysql connection string is not parsed properly

[rutkai]

Data

• Shiori version: v1.5.5
• Database Engine: mysql
• Operating system: linux
• CLI/Web interface/Web Extension: NA

Describe the bug / actual behavior

You cannot provide a mysql connection string that is accepted by both the driver and the application.

The problem is that it parses the connection string looking for a schema, but it won't be stripped from the string that is passed to the driver:
https://github.com/go-shiori/shiori/blob/master/internal/database/database.go#L57

But the driver itself doesn't accept a scheme:
https://github.com/go-sql-driver/mysql#dsn-data-source-name

Furthermore, the new connection string is preferred, but the documentation is still using the old way.

Expected behavior

It connects to mysql instance.

To Reproduce

Steps to reproduce the behavior:

• Use a connection string without a scheme: shiori:passwd@(mysql)/shiori?charset=utf8mb4
• Use a connection string with a scheme: mysql://shiori:passwd@(mysql)/shiori?charset=utf8mb4

Notes

I'll create a PR for it later on. :D