- Use strong_memoize for prometheus_adapter since it can be nil in some
cases.
- Do not phrase spec descriptions with 'should'.

The names can change in different runs of the spec.

- It is now being done in ProxyService class.

The api will proxy requests to the environment's prometheus server.
The Prometheus::ProxyService class can be reused when we add support for
group prometheus servers.

- This is so that we don't have to check that params is of type
ActionController::Parameters in ProxyService.

- Permit params in ProxyService class to avoid having to make changes
to both ProxyService and to PrometheusApiController when adding support
for more prometheus apis.
- Also refactor the cache specs.

- proxyable is a better name for any model object that has a prometheus
server to which requests can be proxied.

- It is unlikely that we will stop supporting prometheus APIs that were
previously supported.

- Add a method for returning a service_unavailable response.
- Keep only one spec to test that the prometheus response is returned
as-is.

- calculate_reactive_cache does not need to initialize @prometheus_owner
again. It's already being initialized in the initialize method.

- The service uses the PrometheusClient.proxy method to call the
Prometheus API with the given parameters, and returns the body and
http status code of the API response to the caller of the service.
- The service uses reactive caching in order to prevent Puma/Unicorn
threads from being blocked until the Prometheus API responds.

- Also refactor the get and json_api_get methods so that the get method
can be reused by the new proxy method.
- The new proxy method makes no changes to the request to the prometheus
server and response from the prometheus server. This allows it to be
used as a proxy to the Prometheus server, hence the name.

Fix capitalization of a sentence in CONTRIBUTING.md

See merge request gitlab-org/gitlab-ce!27021

Backport Resizable container component for gl-charts

See merge request gitlab-org/gitlab-ce!26843

* Fix up graph resize logic if navbar is collapsed

Add snapshot

Resize vuln graph

See merge request gitlab-org/gitlab-ee!10028

Clarify the Runner registration and authentication tokens

See merge request gitlab-org/gitlab-ce!26996

Specify the release that app will be removed from Deploy Boards

Closes #9221

See merge request gitlab-org/gitlab-ee!10607

Merge branch '9217-warn-on-git-fetch-over-ssh-if-the-secondary-is-lagging-the-primary' into 'master'

Display console messages, if available

See merge request gitlab-org/gitlab-ce!26692

Merge branch '9217-warn-on-git-fetch-over-ssh-if-the-secondary-is-lagging-the-primary' into 'master'

Geo: Display secondary replication lag on console (if lag > 0 seconds)

Closes #9217

See merge request gitlab-org/gitlab-ee!10471

Resolve "Hide Kubernetes cluster warning if project has cluster related"

See merge request gitlab-org/gitlab-ce!26749

Fix and expand Gitaly FindCommit caching

See merge request gitlab-org/gitlab-ce!27018