[`Docs`] Fix typos (#7131)
* Add copyright notice to relevant files and fix typos
* Set `timestep_spacing` parameter of `StableDiffusionXLPipeline`'s scheduler to `'trailing'`.
* Update `StableDiffusionXLPipeline.from_single_file` by including EulerAncestralDiscreteScheduler with `timestep_spacing="trailing"` param.
* Update model loading method in SDXL Turbo documentation
