feat: added TextToImageSingle TaskType to the TaskProcessingAPI

[bigcat88]

Summary

We need a default task type for image generation tasks that do not support "count" (which is actually a "batch" parameter)

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[bigcat88]

we decided after discussion, that we do not need this

[github-actions]

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