feat: add core:audio2text:subtitles task type, register file action

[edward-ly]

Registers a file action and adds support for the new core:audio2text:subtitles task type. The OCP\TaskProcessing\TaskTypes\AudioToTextSubtitles class is imported conditionally to maintain compatibility with NC versions older than 35.

To Fix

• This does not seem to have any adverse affect on the tasks themselves, but when opening finished subtitles tasks, the browser currently reports a few errors in the console such as GET https://nextcloud.local/ocs/v2.php/apps/assistant/api/v1/file/104/info returning a 404 status. (done)

Limitations

Currently, the Save this media button for output files automatically appends the .srt extension for .srt files, but not for .vtt files. This seems to be a limitation of the PHP Mimey package as it doesn't recognize the text/vtt MIME type.

By contrast, the Download this media button automatically appends the .vtt extension for .vtt files, but not for .srt files for me. Since the browser/OS looks to be doing the MIME type to extension conversion at that point, I'm not sure if there's anything we can do there.

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

[edward-ly]

Question: do we want to try to maintain compatibility with NC 33 on the main branch, or is it OK to bump min-version up to 35 and remove class_exists and other checks accordingly?

[julien-nc]

I hope you don't mind, I added some changes

• Rebased on main
• Ignore the missing task type class error, it will come in nextcloud/ocp and there are some class_exists checks.
• Use php 8.3 in phpunit action because NC 35 dropped support for 8.2

do we want to try to maintain compatibility with NC 33 on the main branch, or is it OK to bump min-version up to 35 and remove class_exists and other checks accordingly?

It is quite convenient to keep the compatibility with the last 2 or 3 NC versions. If we find a serious bug, we can publish one single release for all the supported NC versions. IMHO let's keep the compatibility with 33 for now.

[edward-ly]

@julien-nc What's the status of this PR right now? Is there anything else that needs urgent fixing?