Add remote database index creation to index creation task

Allows an application to create indexes specifying a different database example amco_sis/db/indexes/bs/legacy_school_id.json

{
  "name" : "grade_subject-grade_code-language-id-json-index",
  "fields": ["legacy_school_id"],
  "db": "bs"
}

In this case the db key is used to specify which database will have the index created, this is used for models such as school.rb

with set_namespace :bs

if db is not specified the default database connection is used

amco / dolly