fix: Fix django.cache service tags for Inferred Services config

[timmc-edx]

This is intended as a temporary workaround until Datadog can put in a proper fix.

---

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]

Please add a link to an issue for cleaning this up. It might even replace the help link, which could be in the issue, and won't be accessible by most people. Thanks.

[timmc-edx]

Ah yeah, I think I meant to link to the Inferred Services issue instead -- I'm going to be mentioning this as a thing to clean up in the A/C of that issue. I'll link there instead in any case.