Clarify input size constraints for gpt-image-2 images

[HenryvanderVegte]

Added note about input size constraints for image generation.

[prmerger-automator]

@HenryvanderVegte : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit 3654841:

✅ Validation status: passed

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articles/foundry/openai/how-to/dall-e.md	✅Succeeded

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[v-dirichards]

@PatrickFarley

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[learn-build-service-prod]

Learn Build status updates of commit 17f53cc:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/foundry/openai/how-to/dall-e.md	✅Succeeded

For more details, please refer to the build report.

[learn-build-service-prod]

Learn Build status updates of commit ea6d714:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/foundry/openai/how-to/dall-e.md	✅Succeeded

For more details, please refer to the build report.

[PatrickFarley]

#sign-off

[prmerger-automator]

@HenryvanderVegte : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.