Bill of Materials - Prelimary Rails implementation

See https://gitlab.com/gitlab-org/gitlab-ee/issues/10075 for full context.

This issue is to track the Rails implementation that will happen in %11.11 to reduce the weight of the final implementation for https://gitlab.com/gitlab-org/gitlab-ee/issues/10075.

Goals

• Put everything behind a feature flag
• Provide mock data in the format that the we agree on for https://gitlab.com/gitlab-org/gitlab-ee/issues/10075
• Provide the API in a way that can be consumed from the FE implementation: https://gitlab.com/gitlab-org/gitlab-ee/issues/11059

Implementation plan

GET /*namespace_id/:project_id/dependencies.json

Params

sort_by=[type, name(default value)]
sort=[desc, asc(default value)]

Response

so if everything is OK, the endpoint returns a bare array:

[
  {
    "name": "rails",
    "type": "gem",
    "location": {
      "blob_path": project_path/blob/commit_ref_of_pipeline/file_path#line_start-line_end,
    },
    "version": "5.2.3",
    "requirements": [
      "~>5.2.3"
    ]
  },
  ...
]

if there is an edge case, the endpoint returns

{  
   "report_status": "file_not_found"||"outdated" (values to be discussed)
}