Allow users to read pipelines for public projects
with public builds enabled without providing an access token.

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.

Used to get the variables via the API endpoint
`/projects/:id/pipelines/:pipeline_id/variables`
Signed-off-by: NAgustin Henze <tin@redhat.com>

- rewords examples starting with 'should'
- rewords examples starting with 'it'

Note: I had to manually fixup "onlies" to "only"

Expose head pipeline for the MR in the api when requesting
related merge requests for an issue and show a detailed
status for the pipeline, which would include:
details_path, favicon, group, icon, label, text, tooltip.

https://gitlab.com/gitlab-org/gitlab-ce/issues/57662#note_152023412

AuditEventService isn't equipped to handle logging of the destruction of
entities such as CI pipelines. It's a project-level event that operates
on a pipeline. The current log doesn't even indicate that the pipeline
is being destroyed.

This is a CE backport of
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9105.  We're
removing the auditing call because it breaks the EE implementation.

Updates specs to use new rails5 format.

The old format:
`get :show, { some: params }, { some: headers }`

The new format:
`get :show, params: { some: params }, headers: { some: headers }`

Move all logic for destroying a Pipeline into a service so it's easily
reusable.