Add xadapter support

[umisetokikaze]

The codebase for xadapter was recently made public. Although I'm not an engineer and cannot grasp the details, it seems possible to maintain compatibility between XL and 1.5, such as with Lora. Additionally, it appears to support controlnet right from the samples. Hence, I'd like to request the implementation of native support or an extension for xadapter in sd-forge.

https://github.com/showlab/X-Adapter/tree/main?tab=readme-ov-file

[huchenlei]

Already tracked by #290