Reduce middleware dependence

[tobytwigger]

Currently, the middleware must be run in the order

\Linkeys\UrlSigner\Middleware\AddLinkToRequest,
\Linkeys\UrlSigner\Middleware\AddLinkDataToRequest,
\Linkeys\UrlSigner\Middleware\CheckLinkUnchanged,
\Linkeys\UrlSigner\Middleware\CheckLinkValid

This could cause an issue since middleware order cannot be enforced.

Suggested Solution:

• Resolve the link from the request in AddLinkDataToRequest, CheckLinkUnchanged, CheckLinkValid to remove dependency on AddLinkToRequest.