Add more information for distributed tracing

[xxx7xxxx]

Background

The tracing information only contains http server and pipeline name as different span. It's hard to debug when it comes to more details.

Proposal

1. Add some standard information such as path, method to tags payload.
2. Support config to add user-defined tags, e.g:

kind: HTTPServer
name: http-server-example
port: 10080
tracing:
  serviceName: httpServerExmple
  zipkin:
    hostport: 0.0.0.0:10080
    serverURL: http://localhost:9412/api/v2/spans
    sampleRate: 1
    sameSpan: true
    id128Bit: false
    tags:               # +
      MyTagKey: X-Value # +
rules:
  - paths:
    - pathPrefix: /pipeline
      backend: http-pipeline-example

[samutamm]

This is a good idea. I agree that http.path and http.method are good standard tags to include by default and the rest can be supported by user defined tags. Opentracing-go span.SetTag can be used to add the tags.

[samutamm]

I would move the custom tags to same level as zipkin entry, as they are not necessary zipkin specific. Like this:

kind: HTTPServer
name: http-server-example
port: 10080
tracing:
  serviceName: httpServerExample
  tags:                 # +
      MyTagKey: X-Value # +
  zipkin:
    hostport: 0.0.0.0:10080
    serverURL: http://localhost:9412/api/v2/spans
    sampleRate: 1
    sameSpan: true
    id128Bit: false
rules:
  - paths:
    - pathPrefix: /pipeline
      backend: http-pipeline-example