Support Header matching in Endpoint Routing

### Is your feature request related to a problem? Please describe.
No. In the context of YARP, some routes must support header matching. If there is interest, I can submit a PR to contribute that here.

### Describe the solution you'd like
Our implementation handles the following:
* Match on the presence of a given header
* Match on a given value of a header (e.g. only match if header `x-example` has value `abc`, `def` or `ace`. Custom string comparison modes are supported)
* Match on a given prefix of a header value (e.g. only match if header `x-eample` starts with `abc`, `def` or `ace`. Custom string comparison modes are supported).

### Additional context
We have not implemented jump tables yet. We would hope the ASP .NET Core can take that on down the line if it seems relevant.