Extend capabilities of "X-IP" header

In order to extend the capabilities of the Octavia project, we suggest adding the following HTTP headers:
- X-Client-IP
- X-Forwarded-IP
- X-Real-IP

The demand for these headers is driven by the need to seamlessly integrate Octavia with existing legacy systems that rely on handling of client IP addresses. Introducing support for these headers bridges the gap between legacy infrastructure and modern cloud technologies, ensuring a smooth transition and continued functionality for organisations operating in hybrid environments.

Here are some examples of technologies that make use of these headers:

- The X-Forwarded-IP header is commonly used to identify IP address of the user connecting to the e-mail server via HTTP mail service.

- The examples in the Nginx documentation often recommend using the X-Real-IP header to pass the real IP address of the client.

- In the examples Apache shows the X-Real-IP and X-Client-IP headers to determine the real IP address of the client for logging and command execution.