[FEATURE]

## Is your feature request related to a problem? Please describe.
Unable to set the `--tracing-backend` option on our k8s agent stack

## Describe the solution you'd like
Add support for specifying a `tracing-backend` in the `agent-config` schema of a k8 agent stack.

## Affiliation (optional)
Faire Wholesale Inc.

Start by locating the agent-config schema used by the Kubernetes agent stack and inspect how existing agent options are represented. Trace where the --tracing-backend option is handled, then verify that the schema accepts tracing-backend and that the configured value reaches the agent stack.

Written by the indexing model from the issue text.