Separate setup part from entrypoint script

[strarsis]

When a service/startup manager (e.g. chaperone) should
be used, the startup with pid check/restarting is handled by it instead.

The setup part in the entrypoint script (that runs sh scripts or import sql dump files) should
be separately callable by the startup manager as service dependency, without starting mysqld.

[yosifkit]

This is possible with the customization added in #471. For example, just doing the initialization parts: #423 (comment).