Change highlights log message level to DEBUG

[farshidz]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Improvement

• What is the current behavior? (You can also link to an open issue here)
  Where attributes_to_retrieve excludes a searchable attribute, Marqo prints a warning because retrieved fields aren't enough to generate highlights. This warning is per result, so for limit=1000 it's printed 1000 times. In production, this has led to high CPU util and 1s+ post-processing telemetry (i.e. result processing in Marqo).

• What is the new behavior (if this is a feature change)?
  Change log level to DEBUG for this message

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No

• Have unit tests been run against this PR? (Has there also been any additional testing?)
  NA

• Related Python client changes (link commit/PR here)
  NA

• Related documentation changes (link commit/PR here)
  NA

• Other information:

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added / updated (for bug fixes / features)