Document that date math is locale independent
Document that date math is locale independent

With this commit we add a note to the API conventions documentation that
all date math expressions are resolved independently of any locale. This
behavior might be puzzling to users that try to specify a different
calendar than a Gregorian calendar.

Closes #37330 
Relates #37663
robin13/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,scorpionvicky/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,HonzaKral/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,coding0011/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,HonzaKral/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch