MINOR: Reduce repetitive logs on large queries by adjusting connection logging

[Dugong42]

Problem

Connectors produce too many (100+/s) repetitive connection logs when querying a large number of rows.

A message is logged by the CachedConnectionProvider for each fetching of rows regardless of whether a new connection is created or the existing connection is used:

Database connection established

See #1493

Solution

The repetitive log has been moved to the CachedConnectionProvider.newConnection() method to only record new connections.

Access to the CachedConnectionProvider is logged as DEBUG when an existing Connection is used.

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[Dugong42]

As it is recommended to back-port fixes to earlier branches, I'm submitting this change to the 10.6 branch.
However there'll be a small conflict when merging to 10.7, as the log message that I modified was changed from DEBUG to INFO on that branch.

[Dugong42]

Hi, any chance for a review ? :)
@rajdangwal
Thanks!