Wire up DiagnosticsHandler (dotnet#456)

* Wire up DiagnosticsHandler

* Remove deprecated events

* Fix broken tests

* Add a toggle to the HttpClientOptions

* Add short-circuit if not enabled

* Remove existing header if we already have a parent

* Fixes after rebasing

* Greatly simplify DiagnosticsHandler

* Further simplification

* Yet even simpler

* Rename to ActivityPropagationHandler
Fix comments

* Update src/ReverseProxy/Telemetry/ActivityPropagationHandler.cs

Co-authored-by: Chris Ross <Tratcher@Outlook.com>

* Make PropagateActivityContext nullable

* Fix TODO in test

* Fix PR comments

* Add ActivityPropagationHandler test

* Add missing using

* Made handler public so that it can be re-used

* Moved test to appropriate folder

* Fix namespace

Co-authored-by: Chris Ross <Tratcher@Outlook.com>
Co-authored-by: MihaZupan <mihazupan.zupan1@gmail.com>

Mitigation of wrong cookie value separator (dotnet#451)

Implement Equals for ProxyRoute & Cluster (dotnet#366)

* Implement Equals for ProxyRoute & Cluster

* Add copyright license

* Address review points

* Fix test merge conflicts

Co-authored-by: Chris Ross <Tratcher@Outlook.com>

Add order to RouteEndpoint (dotnet#360)

Disable official builds for unix (dotnet#341)

Rename Backend to Cluster (dotnet#251)

* Rename Backend to Cluster

* Remove OrNull

* Update docs/docfx/articles/getting_started.md

Co-authored-by: Stephen Halter <halter73@gmail.com>

Co-authored-by: Stephen Halter <halter73@gmail.com>

Output runtime versions during benchmark startup (dotnet#170)