doc: use sphinx-autoapi for API reference

[moe-ad]

This PR is related to ansys-internal/pyansys-planning#100. The migration of the API documentation migration is being handled here.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.96%. Comparing base (af30b32) to head (7d80e67).

Additional details and impacted files

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- Coverage   88.37%   85.96%   -2.41%     
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  Files          89       89              
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- Hits         9059     8812     -247     
- Misses       1192     1439     +247     

[moe-ad]

@jorgepiloto, something I need to mention (already discussed with Revathy about this too).
If you try to build with sphinx 7.1.0 (which is the current default on this repo) while having autoapi enabled, the build fails. We narrowed it down to app.confdir being a str object in sphinx 7.1.0 and a path object in sphinx 8.1.3.

In ansys-sphinx-theme 1.2.2 (which is the current default on this repo), the autoapi extension treats app.confdir correctly (as a path object) but using sphinx 7.1.0 will result in an error because of the above reason.

In order words, we need sphinx 8.1.3 to be enforced moving forward.

[jorgepiloto]

Thanks for the research, @moe-ad. Then, let's focus on updating the rules for the moment. After that, we can update the examples to Jupytext. This should allow us to revisit the complete set of examples, making sure they run without random failures. Luckly, we can migrate to the latest Sphinx after that and merge this.