feat: disable edxapp legacy browser in newrelic.ini.j2 stage and edge

[robrap]

---

Make sure that the following steps are done before merging:

• Have a Site Reliability Engineer review the PR if you don't own all of the services impacted.
• If you are adding any new default values that need to be overridden when this change goes live, update internal repos and add an entry to the top of the CHANGELOG.
• Performed the appropriate testing.

[robrap]

@timmc-edx:

1. Do you know if there is any way to easily make this configurable per environment (e.g. stage, or edge)?
2. If not, should we just pause the pipeline and ensure that Stage seems happy, and then rollout to Edge+Prod?
3. Other ideas?

[timmc-edx]

For a hacky approach we could refer to the environment via Ansible variables in that .j2 file.