Issue 30 tcp http support

[ciroque]

Proposed changes

This change introduces a layer between the Synchronizer and the Border Servers (NGINX Plus running outside the Cluster in our main use case). It further supports Annotations on the Service that determine if the Upstream to be updated is a Stream ("tcp"), or HTTP ("tcp") Upstream block.

The Annotations are key/value pairs on the Service itself, the key is the Port Name (and the Upstream name at this time), and the value is one of "tcp" or "http". A value other than these results in a NullBorderClient implementation being created (to avoid panics). An accompanying error indicates the problem. Check your errors...

"TCP" will update the Border Servers using the Update/DeleteStreamUpstreamServers methods on the NGINX Plus client.

"HTTP" will update the Border Servers using the Update/DeleteHttpUpstreamServer methods on the NGINX Plus client.

This implementation also provides a foundation on which other Border Servers can be created. **This is not a goal of the project at present.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)

[chrisakker]

I see an typo in the Proposed changes, paragraph 4:
"HTTP" will update the Border Servers using the Update/DeleteHttpServer methods on the NGINX Plus client.
Should be:
"HTTP" will update the Border Servers using the Update/DeleteHttpUpstreamServer methods on the NGINX Plus client.