Add env_var and file as supported types for CI variables. Variables of
type file expose to users existing gitlab-runner behaviour - save
variable value into a temp file and set the path to this file in an ENV
var named after the variable key.

Resolves https://gitlab.com/gitlab-org/gitlab-ce/issues/46806.

It also renames the API::PROJECT_ENDPOINT_REQUIREMENTS constant to
API::NAMESPACE_OR_PROJECT_REQUIREMENTS

Partially addresses #47424.

Had to make changes to spec files because
stubbing methods on frozen objects is a mess
in RSpec and leads to failures:

https://github.com/rspec/rspec-mocks/issues/1190

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2112

Always use declared_params(include_missing: false)
so that we don't give nils for optional arguments

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

This MR simplifies CI permission model:
- read_build: allows to read a list of builds, artifacts and trace
- update_build: allows to cancel and retry builds
- create_build: allows to create builds from gitlab-ci.yml (not yet implemented)
- admin_build: allows to manage triggers, runners and variables
- read_commit_status: allows to read a list of commit statuses (including the overall of builds)
- create_commit_status: allows to create a new commit status using API

Remove all extra methods to manage permission.
Made all controllers to use explicitly the new permissions.