[FEATURE] Make raw JSON REST requests to OpenSearch

[dblock]

Is your feature request related to a problem?

Coming from opensearch-project/opensearch-clients#62, add support for making raw JSON requests.

What solution would you like?

Add a high level DSL, e.g. client.get and client.post.

Do you have any additional context?

Some of this may already be implemented under #331. At the very least we need documentation that doesn't use any high level DSL methods.

[Jakob3xD]

This can already be done by using the Perform function of the client.

opensearch-go/opensearch.go

Line 265 in f4a8446

func (c *Client) Perform(req *http.Request) (*http.Response, error) {

You just need to build/ create the http request by your self.

[dblock]

@Jakob3xD thanks, we just need to document this and provide a working sample ;)