Prior to this commit, Spring's SchedulerFactoryBean always set the
"org.quartz.jobStore.class" property to LocalDataSourceJobStore even if
the user had already specified a custom JobStore implementation via the
Quartz properties file or Properties object, thereby effectively
ignoring the user configuration.
This commit addresses this by configuring Quartz to use Spring's
LocalDataSourceJobStore only if a JobStore has not already been
specified via user configuration.
Closes gh-27560