Provide a way to configure Jaeger Agent HTTP Port

[joe-elliott]

Support for Jaeger Remote sampling was added in this PR: #448 but provides no way to configure the listening port. As such the http proxy is never started.

This is the struct var that can not be set:

opentelemetry-collector/receiver/jaegerreceiver/trace_receiver.go

Line 65 in b468dee

AgentHTTPPort int

I can quickly fix this, but would like to like to merge #490 first as they are both touching the Jaeger receiver configuration code.

@annanay25 👋