feat: added parameter to respect altered target

[DanielRailean]

About the PR

This PR builds upon #41 as it improves the compatibility with other Kong plugins which might alter the target host/port, specifically when the overwrite_target_host or overwrite_target_port are also used.

In essence, it adds the possibility of a 'soft' override, which means it will only occur if not already overridden by other plugins.

Screenshots

Changelog

• Add: the use_altered_target boolean config parameter, maintaining backwards compatibility
• Closes: Use aws-request-signing in combination with other kong plugins, such as canary release #40

Testing

• Has been tested locally.