This commits adds support for metrics dashboards
for embedding. If the flag 'embedded' is provided
to the environments/id/metrics_dashboard endpoint,
the response will be suitable for embedding in
issues or other content.

This is a precursor for support for embedding
metrics in GFM.

Updates the EnvironmentController#metrics_dashboard endpoint
to support a "dashboard" param, which can be used to specify
the filepath of a dashboard configuration from a project
repository. Dashboard configurations are expected to be
stored in .gitlab/dashboards/.

Updates dashboard post-processing steps to exclude custom
metrics, which should only display on the system dashboard.

When showing the HTML version of the environment metrics we don't need
to fetch their metrics because we don't use them anymore on the HTML
version.

We use additional_metrics.json endpoint now.

Change MetricsDashboard::Service to inherit from BaseService so that
it can reuse methods like initialize, success, error.

Adds frozen string to the following:

* spec/bin/**/*.rb
* spec/config/**/*.rb
* spec/controllers/**/*.rb

xref https://gitlab.com/gitlab-org/gitlab-ce/issues/59758

We're moving from using terminology related to terminals when
we refer to Websockets connections in Workhorse.
It's more appropiate a concept like channel.

Adds support for start and end parameters in the #additional_metrics
endpoint of the EnvironmentsController. start and end are meant to be
unix timestamps, per the Prometheus API (as the consumer of this
endpoint will eventually be transitioned to a prometheus endpoint).
This functionality is behind the :metrics_time_window feature flag
for development.

It's needed to show shorter names in environments "folders"

Add changelog

Rename word to query

User hash for limit

Do not allow control limit

Rename pluck names and add more specs

To support environment folders in the UI on the Environments List
page, the environments index route previously returned one environment
per folder, excluding those other than the latest deploy. However, the
environtments dropdown on the metrics dashboard requires that any
environment be selectable.

To accommodate both use cases, support an optional 'nested' parameter
in the index route to return either a flat, complete response or a
nested response based on the use case in question. The new default
response structure is the flat response.

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 }`

In EE we redefine Environment#terminals, which makes it impossible to
use `allow_any_instance_of(Environment)` or
`expect_any_instance_of(Environment)`. Other approaches of stubbing
this class, such as by stubbing `new`, only result in spec failures.

To solve this issue, we add a simple `defined?(EE)` check in the tests
to change the thing that we are testing. This is rather obnoxious,
because it requires EE knowledge in CE, and can break if
`EE::Environment` is removed without updating CE. Unfortunately, it
appears to be the only solution we have apart from modifying these tests
in EE (which would cause merge conflicts).

Specify environment actions to distinguish between metrics and every other environment related actions

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

The decision was made around:
https://gitlab.com/gitlab-org/gitlab-ce/issues/26407#note_30624641

Rename other URL generators

admin_builds_path -> admin_jobs_path

Fix tests and more renaming

Fix more tests

Also change build_id to job_id in the controller

Fixes gitlab-org/gitlab-ce#30814

For the index view, the environments can now be requested every 15
seconds. Any transition state of a projects environments will trigger a
cache invalidation action.

Fixes gitlab-org/gitlab-ce#31701