Mirage is Injecting the appbase Bearer Authorization token into non-appbase Elasticsearch cluster requests

This is the cause of #16

Reproduction steps:
- Install mirage as an extension or run it locally.
- Provide an AWS-hosted ElasticSearch cluster URL and index.
- Note in the web inspector of your choice that the request to `${host}/${index}/_mapping` includes an `Authorization` header, which causes the request to fail.
- This Authorization header should not be sent.

Reproduce the request to `${host}/${index}/_mapping` with an AWS-hosted Elasticsearch URL and inspect its headers in a web inspector. Trace where the Authorization header is added to Elasticsearch requests; done means non-appbase cluster requests no longer include the appbase Bearer token and the mapping request succeeds.

Written by the indexing model from the issue text.