use script_path for webui root in launch_utils

[w-e-w]

Description

webui modules like launch to be imported correctly in extensions install.py when user run webui from a different cwd then webui root
fix

• [Feature Request]: Extentions can't use A1111 modules in correct way #15697

more sensible implementation of what is trying to achieve

• fix: correct PYTHONPATH for extentions installation proccess #15704

script_path is difined relative to modules/paths_internal.p so won't be affected by cwd like the current os.path.abspath('.')

stable-diffusion-webui/modules/paths_internal.py

Lines 16 to 17 in 1c0a0c4

	modules_path = os.path.dirname(os.path.realpath(__file__))
	script_path = os.path.dirname(modules_path)

additional
also change the path for CHANGELOG.md

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests