feat: #3634447 Add an Audio generator: speech read from the text with the text to speech provider

Issue: https://www.drupal.org/project/ai_media/issues/3634447

A new audio generator: the text is read aloud by the text to speech provider and saved into a media type with the Audio file source, in a voice the model lists; mp3, wav or aac. Off by default, like Video.

Also in this MR, because the generator needs them: a generator may name its text field (field_title, field_help on the attribute: "Text to speak"); a sound or video result shows a player and its link reads "Open in a new tab"; only an image is asked for alt and title, so other types make one AI call less.

Checked: phpcs, phpstan, the kernel suite (91 tests, 4 new), and a real generation with OpenAI tts-1 on the dev site: a 67 KB MP3 in 15 seconds, played, saved. The e2e scenario runs on Add media with the Echo provider, which speaks too.

AI-Generated: Yes

Checkpoints:

• File an issue
• Addition/Change/Update/Fix
• Testing to ensure no regression
• Automated unit testing coverage
• Automated functional testing coverage
• UX/UI designer responsibilities
• Readability
• Accessibility
• Performance
• Security
• Developer Documentation
• User Guide Documentation
• Reviewed by human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Release notes snippet
• Release

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