ESClient method spec

[siddharthlatest]

Follow a signature similar to the JS client we have here - https://docs.appbase.io/javascript/api-reference.html#appbase.

https://github.com/harsh-2711/SwiftElasticSearch/blob/bf20eec8bec88b48edbe16929af50684d14c90d9/SwiftElasticSearch/SwiftElasticSearch/SwiftElasticSearch.swift#L119

• username, password are redundant parameters for credentials.

• We shouldn't ask for sslconfig from the user.

[siddharthlatest]

url should also take the scheme from the user. Example value can be: "https://elasticsearch:9200"