[dotnet] Changelog updated for RC 2

[dotnet] Update supported version of CDP to 93, remove 91

[grid] Doing `.countDown()` when the right event has been listened to

Avoiding running tests for changed referrer header behaviour on firefox

Add missing target to Rakefile

Amend java release targets

Adding support for CDP version 87 in .NET

[py] Bump version to 4a6

Updating .NET tests

[java] Switching default client implementation from okhttp to netty