Create callback request returns 200

[dfarr]

When a request to create a callback is made against a promise that is already completed, the response will contain a 200 code along with the promise information. The caller can use this information to immediately continue. The 200 response code contrasts to a 201 that is returned in the case where the promise is pending and a callback is created.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 57.20%. Comparing base (e5cdc6e) to head (8175fa1). Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/app/coroutines/completePromise.go	84.61%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #406 +/- ## ======================================= Coverage 57.19% 57.20% ======================================= Files 113 113 Lines 10364 10364 ======================================= + Hits 5928 5929 +1 + Misses 4005 4004 -1 Partials 431 431 ```

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