fix: repair how multiple examples are declared in web_api

[joanise]

Before fastapi 0.99, we could declare multiple examples with

examples=[{"key1": ..., "key2": ...}]

Now, examples no longer accept keys or metadata, just a list of plain examples.

Since fastapi 0.103, using openapi_examples instead restores the old key and metadata functionality.

See https://fastapi.tiangolo.com/tutorial/schema-extra-example/#using-the-openapi_examples-parameter for details.

PR Goal?

Make the examples for /assemble work again on https://readalong-studio.herokuapp.com/api/v1/docs#/default/assemble_assemble_post

Fixes?

Currently, the proposed example is invalid:

This PR brings it back to what we used to have:

Feedback sought?

sanity checking

Priority?

low

Tests added?

n/a

How to test?

    pip install uvicorn
    cd readalongs/
    DEVELOPMENT=1 uvicorn readalongs.web_api:web_api_app --reload

then navigate to
http://localhost:8000/api/v1/docs#/default/assemble_assemble_post
and see the two examples being proposed instead of the big invalid block.

Confidence?

high

Version change?

no

[semanticdiff-com]

Review changes with SemanticDiff.

Analyzed 1 of 2 files.

Overall, the semantic diff is 95% smaller than the GitHub diff.

	Filename	Status
❔	requirements.min.txt	Unsupported file format
✔️	readalongs/web_api.py	94.2% smaller

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.12%. Comparing base (3cab240) to head (3fe116b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #243   +/-   ##
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  Coverage   87.12%   87.12%           
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  Files          21       21           
  Lines        1786     1786           
  Branches      323      323           
=======================================
  Hits         1556     1556           
  Misses        191      191           
  Partials       39       39           

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