SDXL demo: consistent opt shape and seed (#18445)
### Description
A few refinements:
(1) Use fixed optimized shape for dynamic engine of TRT.
(2) Use same seed in base and refiner.
(3) Save metadata to png file so that it is easy to reproduce.
(4) Disable EulerA scheduler for XL since it has issue in refiner with 1.16.2.
(5) Limit height and width to be divisible by 64.
(6) Update document to add a link of downloading optimized model.
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Co-authored-by: kunal-vaishnavi <115581922+kunal-vaishnavi@users.noreply.github.com>
