Opentelemetry span name

[ashishb-solo]

Description

Implement control plane API for modifying span names for tracing purposes.

Context: https://github.com/solo-io/envoy-gloo/pull/368

API changes

Add span_transformer.name to the transformation filter.

Code changes

Ensure that the span_transformer field is copied from the Gloo API to the Envoy API

CI changes

None

Docs changes

TODO: we should update https://docs.solo.io/gloo-edge/latest/guides/traffic_management/request_processing/transformations/ to explain that transforms can also modify traces.

Context

This is an incremental update to implementing a control plane API for updating the span name for opentelemetry traces.

Interesting decisions

Testing steps

Notes for reviewers

Checklist:

• [X] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [X] I have added tests that prove my fix is effective or that my feature works