Managed applications template artifact

What does this MR do?

Takes the JSON formatted of helm ls --output json, and uses the contents to update the status of each application.

Limited only to prometheus for now.

feature flag: cluster_applications_artifact

Related issue: #35672 (closed)

Screenshots

This is what Prometheus looks like when it's installed externally (via CI/CD).

Issues (to follow-up in #35672 (closed))

• Prometheus is grayed out because Helm is not installed
• Helm is actually installed but has a status: 0. This is due to application_status#97:

> h = Clusters::Applications::Helm.find 42
  Clusters::Applications::Helm Load (0.8ms)  SELECT "clusters_applications_helm".* FROM "clusters_applications_helm" WHERE "clusters_applications_helm"."id" = $1 LIMIT $2  [["id", 42], ["LIMIT", 1]]
=> #<Clusters::Applications::Helm:0x00007fc6972c5690
 id: 42,
 cluster_id: 56,
 created_at: Wed, 13 May 2020 12:36:39 UTC +00:00,
 updated_at: Fri, 15 May 2020 02:15:12 UTC +00:00,
 status: 0,
 version: "2.16.6",

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done