Docs: Added 'd' to the list of supported units.
Docs: Added 'd' to the list of supported units.

Day was missing from the list of supported units in the date math section.

Closes #8151

fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch