[Doc] clarified the usage of and settings

[andsel]

Release notes

Clarified the usage of jdbc_validation_timeout and connection_retry_attempts_wait_time settings.

What does this PR do?

Improve the documentation description of a couple of configs.
The connection_retry_attempts_wait_time is used as retry mechanism only at Sequel Database object creation, so at connection pool time creation, during the registration of the plugin.
The jdbc_validation_timeout is used by Sequel to decide to validate or not a connection when it's borrowed from the pool. If the connection hasn't received or sent data for more than this timeout then a "ping query" is executed; but it doesn't actively executes the ping queries when the connections are in the pool, just on the borrow action.

• code ref to check how connection_retry_attempts_wait_time is used
• code ref to check how jdbc_validation_timeout is used in Sequel.

Why is it important/What is the impact to the user?

Avoid to set not aligned expectations on the usage of these settings.

Checklist

• My code follows the style guidelines of this project
• [ ] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files (and/or docker env variables)
• [ ] I have added tests that prove my fix is effective or that my feature works