Add x-elastic-internal-origin header to all places that make requests to Elasticsearch

[jsvd]

The Logstash Elasticsearch output plugin makes HTTP requests to the following Elasticsearch endpoints:

GET /
HEAD /
GET /_license
POST _bulk?filter_path=..
HEAD /_index_template/<index_name>
PUT /_index_template/<index_name>
HEAD /<index_name>
PUT /<index_name>
GET /_ilm/policy/logstash-policy
PUT /_ilm/policy/logstash-policy
GET /_nodes/http (sniffing)

Notes:

parent setting no longer works (probably hasn't for a long time)

Each of these calls should include the x-elastic-internal-origin header to the HTTP request made to Elasticsearch