Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NRémy Coutable <remy@rymai.me>

FIxes #19361, #3119.

Browser interface allows forking to an owned grup.
This commit brings API up to speed by providing optional namespace
parameter to fork API. This allows forking to users and groups under
forker's control using their id or unique name.

Fixes #21591

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The wrong example for "Branches".
Added option parameters in protect branch section.
Here is reason: https://gitlab.com/gitlab-org/gitlab-ee/commit/3ab07b8aae8dae43cfa3aae1306c59ea264a8594

Maybe this section could/should be deleted. Because in file repositories.md it had been deleted:  https://gitlab.com/gitlab-org/gitlab-ee/commit/8f3701eff005aeedcebff8ce02074f5056a369b3

Also, mutualize AccessRequests and Members endpoints for Group &
Project.
New API documentation for the AccessRequests endpoints.
Signed-off-by: NRémy Coutable <remy@rymai.me>

Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Introduced into the API in e80e3f53

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Also the specs have a minor improvement. Mainly the access right spec.
Changes are reflected in the docs

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>