add script to generate the openapi.json file

[imaitland]

Required if this pipeline for publishing the evolver-ng-ts-client npm package is adopted.

We're actually not likely to do this. Instead the generated openapi.jsonwill likely be just copied into a /ui dir in this project where the frontend will live. The frontend build process (npm) will take care of generating the client from there.

[codecov[bot]]

Codecov Report

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

Project coverage is 95.72%. Comparing base (928941b) to head (173c9e3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #101 +/- ## ======================================= Coverage 95.72% 95.72% ======================================= Files 18 18 Lines 679 679 ======================================= Hits 650 650 Misses 29 29 ``` | [Flag](https://app.codecov.io/gh/ssec-jhu/evolver-ng/pull/101/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ssec-jhu) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/ssec-jhu/evolver-ng/pull/101/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ssec-jhu) | `95.72% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ssec-jhu#carryforward-flags-in-the-pull-request-comment) to find out more.

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