internal/dag: Enable additional fields in Condition

[stevesloka]

Describe the solution you'd like An httplb can contain [conditions](https://github.com/heptio/contour/blob/master/apis/projectcontour/v1alpha1/httploadbalancer.go#L44), as an Include or as part of a Route definition. Currently, we've implemented pathPrefix, but there are additional items to implement:

• [x] HeadersMatch
• [x] HeadersContain
• [x] ExactMatch: https://github.com/heptio/contour/blob/master/design/routing-design.md#exact-path-routing
• [ ] Wildcard Path (i.e. Glob routing): https://github.com/projectcontour/contour/blob/master/design/routing-design.md#path-wildcard

[davecheney]

Sadly we won't be delivering prefix: wildcard condition for Contour 1.0. The design is close from a user facing perspective, but there are some subtle implementation details that remain unanswered and we want to proceed carefully there in case we paint outselves into a corner.

I'm moving this ticket to the backlog as a placeholder for a epic ticket which will capture the business requirements for wildcard routing.

[sunjayBhatia]

removing important-soon as this is an httplb issue, not httpproxy