Add EventSource events

[kichalla]

Events:

• Connection Id (to establish correlation with the current request)

[kichalla]

@davidfowl @rynowak @shirhatti

[muratg]

cc @shirhatti

[muratg]

See the work done in Hosting for adding EventSource: aspnet/Hosting#883

[halter73]

I think it might be possible to implement this on top of logging scopes once we do #640.

[natemcmaster]

Drafting a list of events we should include. Please add more if you want them

• ConnectionStart:
  • connectionId
  • serverAddress
  • localEndPoint
  • remoteEndPoint

[muratg]

@shirhatti Could you review Nate's list?

[natemcmaster]

For cross reference, here are the items we send to ILogger: https://github.com/aspnet/KestrelHttpServer/blob/e55c62444bdd34274173b011720c03f23c4db2f5/src/Microsoft.AspNetCore.Server.Kestrel/Internal/Infrastructure/KestrelTrace.cs