Set db.pool.config.* default values in application.properties

[bs352]

As per issue submitted to the main nacos repostory:
alibaba/nacos#11252

I was experiencing a failure of initialization of the embeded derby database during startup on a somewhat slow machine.

After some digging, it appears the connection timeout is changed from 30s to 3s around version 2.2.1. While the main nacos project contains a default application.properties file that overrides the timeout back to 30s, the modified version for docker image in this repository does not have db.pool.config.* properties.

May I suggest that we add db.pool.config.* properties into application.properties with sensible defaults, and add documentation to include these properties.