Log TIMELINE summaries at the debug level

[djsagain]

NOTE: this was reverted by #13698

Description

At the info level, they represent more than half the log
lines in many tests.

Is this change a fix, improvement, new feature, refactoring, or other?
Minor logging change.
Is this a change to the core query engine, a connector, client library, or the SPI interfaces? (be specific)
Core engine
How would you describe this change to a non-technical end user or system administrator?

Related issues, pull requests, and links

Documentation

(x) No documentation is needed.
( ) Sufficient documentation is included in this PR.
( ) Documentation PR is available with #prnumber.
( ) Documentation issue #issuenumber is filed, and can be handled later.

Release notes

(x) No release notes entries required.

[hashhar]

cc: @nineinchnick since he did some work in past to reduce logs.

[hashhar]

This could've been limited to be a test-only change instead of applying generally to the entire engine.

[findepi]

followed up (reverted) in #13698