Add support for application/soap+xml error handling

[vanny96]

Description

Currently, Tyk returns a JSON response when a request with Content-Type "application/soap+xml" incurs in an error. Added support to return XML instead.

Related Issue

https://github.com/TykTechnologies/tyk/issues/6602

How This Has Been Tested

Not tested

Types of changes

• [x] 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

• [x] I ensured that the documentation is up to date