Support full int8 quantization for diffusers

[l-bat]

What does this PR do?

• Enable full quantization of denoiser models of Stable Diffusion pipelines via optimum-cli.
• Supported --quant-mode options: int8, f8e4m3, f8e5m2.
• Example command is below.

optimum-cli export openvino -m stabilityai/stable-diffusion-2 --quant-mode int8 --dataset conceptual_captions --num-samples 32 --smooth-quant-alpha 0.9 ./sd2

Fixes # (issue)

• 163715

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[l-bat]

@AlexKoff88, @nikita-savelyevv please take a look

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[AlexKoff88]

@IlyasMoutawwakil, @echarlaix, please take a look.

[AlexKoff88]

@IlyasMoutawwakil, @echarlaix, the PR is ready for your review