Support text processing APIs

[ChristophWurst]

Describe the feature you'd like to request

As a Nextcloud app developer I want to experiment with different AI backends for text processing.

Describe the solution you'd like

Implement the APIs of nextcloud/server#38578 / nextcloud/server#38854 so OpenAI can provide text summaries etc.

Describe alternatives you've considered

N/a

[julien-nc]

Will do asap 👍 . First provider which will be implemented: Summarizing with OpenAI's ChatGPT (or LocalAI).
If tests are conclusive, there will also be "extract outline" and "extract topics" text processing providers.

[ChristophWurst]

Merci !

[julien-nc]

Done and released. 4 providers: FreePrompt, Headline, Summarize and Reformulate