#9299 Fix duplicated root path in webassets

[Zharktas]

Fixes #9299, #5615, #7369

Proposed fixes:

root_path gets added in toolkit.py and during rendering in

ckan/ckan/lib/webassets_tools.py

Lines 137 to 138 in d737ad3

	# Add `site_root` if configured
	urls = [url_for_static_or_external(url) for url in bundle.urls()]

This removes it from toolkit.py, as core assets are functioning correctly.
Also updates docs which closes couple related issues.

Features:

• includes tests covering changes
• includes updated documentation
• includes user-visible changes
• includes API changes
• includes bugfix for possible backport

Please [X] all the boxes above that apply

[ckanbot]

Successfully created backport PR for dev-v2.11:

• [Backport dev-v2.11] #9299 Fix duplicated root path in webassets #9301

[ckanbot]

Successfully created backport PR for dev-v2.10:

• [Backport dev-v2.10] #9299 Fix duplicated root path in webassets #9302