Add content pack support for index field type profiles

From support issue: https://github.com/Graylog2/support/issues/61

### What?
the ability to have Index Templates included into Content
Packs
### Why?
It's an awesome feature and I would like to copy one template
from one Graylog to another

(created from Zendesk ticket #626)
gz#626

## Your Environment

* Graylog Version:
* OpenSearch Version:
* MongoDB Version:
* Operating System:
* Browser version: