[bp/1.27] Datadog: restore "resource.name" tag (#30503)

[Smeb]

Hi 👋 - I hope opening a backport like this is the right approach. We would like to have this fix so that we can upgrade to 1.27 in our cluster - without it our trace spans have incorrect names.

I ran the tests locally as follows bazel test --config=libc++ //test. I used libc because my development environment had an unrelated issue with using the stdlib, which I believe is related to #30837.

Commit Message: [bp/1.27] Datadog: restore "resource.name" tag (#30503)
Additional Description:
This is the backport of #30503

Risk Level: low
Testing: local unit tests
Docs Changes: n/a
Release Notes: n/a
Platform Specific Features: n/a
Fixes: #30235

[repokitteh-read-only]

Hi @Smeb, welcome and thank you for your contribution.

We will try to review your Pull Request as quickly as possible.

In the meantime, please take a look at the contribution guidelines if you have not done so already.

🐱

Caused by: #30892 was opened by Smeb.

see: more, trace.