Backport "Fix namespace/project removal elasticsearch limit" to CE

See merge request gitlab-org/gitlab-ce!27933

This is step one of resolving
https://gitlab.com/gitlab-org/gitlab-ce/issues/56838.

Here is what changed:
- Revert the security fix from bdee9e8412d.
- Do not leak repository information (tag name, commit) to guests in API
responses.
- Do not include links to source code in API responses for users that do
not have download_code access.
- Show Releases in sidebar for guests.
- Do not display links to source code under Assets for users that do not
have download_code access.

GET ':id/releases/:tag_name' still do not allow guests to access
releases. This is to prevent guessing tag existence.

When creating a merge request for push options, there may be over 100
queries that are run to create a merge request. Even after we reduce the
number of queries by disabling the Sidekiq jobs, it appears we still
hover near this limit.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/11450

When this option is enabled, GitLab will create namespaces and service
accounts as usual. When disabled, GitLab wont create any project
specific kubernetes resources

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56557

Disallow read user scope to read project events

See merge request gitlab/gitlabhq!3067

Get rid of the user_namespace API helper method

See merge request gitlab-org/gitlab-ce!27636

Inside a wiki, when we show the sidebar or browse to the `pages`,
all page contents are retrieved from Gitaly and that is a waste
of resources, since no content from that pages are going to be
showed.

This MR introduces the method `ProjectWiki#list_pages`,
which uses new wiki_list_pages RPC call to retrieve
pages without content

Also in the `WikisController` we're using the method to show
pages in the sidebar and also on the `pages` page.

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