Add note to docs on whitespace in Log4j settings
Add note to docs on whitespace in Log4j settings

A confusing thing that can happen when configuring Log4j is that
extraneous whitespace throws off its configuration parsing yet the error
messages that arise give no indication that this is the problem. This
commit adds a note to the docs.

Relates #24198

strapdata/elassandra5-rc,strapdata/elassandra5-rc,strapdata/elassandra5-rc,strapdata/elassandra5-rc,strapdata/elassandra5-rc