fix(ui): allow image dims multiple of 32 with SDXL and T2I adapter

[psychedelicious]

Summary

When using T2I Adapter with SDXL base model, images with dimensions that are multiples of 32 are allowed.

Related Issues / Discussions

See https://github.com/invoke-ai/InvokeAI/pull/6342#issuecomment-2109912452 for discussion.

QA Instructions

You should be prevented from Invoking if:

• SD1.5 model selected + T2I Adapter added + image dimensions are not a multiple of 64
• SDXL model selected + T2I Adapter added + image dimensions are not a multiple of 32

Merge Plan

n/a

Checklist

• [x] The PR has a short but descriptive title, suitable for a changelog
• [ ] Tests added / updated (if applicable)
• [x] Documentation added / updated (if applicable)