[TT-13765] add check for host rewrite to DynamicMiddleware (js plugin)

[iamdjones]

Description

Allow hostname rewrite in DynamicMiddleware (mw_js_plugin)

Related Issue

#6791

Motivation and Context

My organization has a use case where we need to route traffic dynamically to a backend hostname based on headers passed into a request. We'd prefer to not manage a GO plugin or it's development environment, and use a custom Javascript plugin instead. However Javascript plugins don't currently allow hostname rewrites.

How This Has Been Tested

Added unit tests provide some coverage. I ran a functional test by building an image and spinning that up as a hybrid data plane node, attached to our tyk hosted control plane. I was able to successfully rewrite the hostname this way.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring or add test (improvements in base code or adds test coverage to functionality)

Checklist

• I ensured that the documentation is up to date
• I explained why this PR updates go.mod in detail with reasoning why it's required
• I would like a code coverage CI quality gate exception and have explained why