Add ability for periodic refreshing of SSL certificate used in database config

[minghay]

What happened: https://github.com/screwdriver-cd/screwdriver/issues/3339 added in the ability to configure the SSL certificate to be used on the database connection, however certificate rotation requires a restart of the server.

What you expected to happen: Add a configuration option to set how frequently an SSL certificate is read into memory so a server restart is not required. The configuration value should be in a value in milliseconds with a default value of 86400000. It should be on the end users to ensure that an SSL certificate is rotated prior to expiration.