Update from ddtrace 1.x to datadog 2.1

[martinemde]

Proposed instead of in addition to #4795 since ddtrace gem has now become datadog as of 2.0.

I attempted to follow this guide.

I didn't see anything else that we're using that was removed, but we'll probably want to double check the integration in staging.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.06%. Comparing base (1755cc7) to head (cb4e3d7).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #4800 +/- ## ======================================= Coverage 97.06% 97.06% ======================================= Files 399 399 Lines 8443 8443 ======================================= Hits 8195 8195 Misses 248 248 ```

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