[FEATURE] Be able to set total number of fields on index

[thejettanderson]

Is your feature request related to a problem?

I cannot using the java client set index.mappings.total_fields.limit on an IndexSettings request, and have to do so manually since my project uses the java client instead of the REST client.

What solution would you like?

I would like to be able to set the total fields limit for an index, same as number of shards, on the IndexSettings object for an IndexTemplateMapping.

What alternatives have you considered?

Using the REST client in addition to the java client, but I really don't want to have to use both clients in my project just so I can set the total fields on an index mapping update.

[wbeckler]

This is worthwhile to fix. Do you want to propose a PR, or at least a method signature?

[VachaShah]

Similar to #379