Network request helper parity

Description

This PR refactors the NetworkRequestHelper's networkResponses data struct to use a 1:many relationship between network requests and responses. This is to support more complex use cases that would rely on multiple requests to the same endpoint.

Before	After
`[TestableNetworkRequest: HttpConnection]`	`[TestableNetworkRequest: [HttpConnection]]`

Also adds a new method in the NetworkRequestHelper: removeAllResponses(for networkRequest: NetworkRequest) Which allows the MockNetworkRequest to maintain the 1:1 network request to response behavior via its own methods to set mock network responses.

Question for reviewers

Please let me know if, for the new method removeAllResponses(for:):
1. Method/parameter name makes sense
2. Method is required to maintain MockNetworkService's API contract to set 1:1 network request to mock response

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

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)

Checklist:

[ ] I have signed the Adobe Open Source CLA.
[ ] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[ ] I have read the CONTRIBUTING document.
[ ] I have added tests to cover my changes.
[ ] All new and existing tests passed.

adobe / aepsdk-edge-ios