CI/CD Quotas - first iteration

Description

This is an issue about first iteration of CI/CD Quotas https://gitlab.com/gitlab-org/gitlab-ee/issues/3477.

General assumptions

• Make it possible to define limits per EE Plan (Plan model)
• Limit both shared and private runners
• When we drop a pipeline, add "Quota exceeded" badge + failure reason on hover
• Make it possible to set limit using a rails console or SQL query in the first iteration
• Make it possible to apply limits to gitlab.com plans, EE subscription plans (EES/EEP) not affected
• Talk with ~Platform about plans regarding Plans and separating EE plans for on-premises plans

Limit number of concurrent pending / running pipelines

• When a pipeline that exceeds limits is about to be created change status to failed, all jobs skipped
• Make it possible to retry this pipeline using Retry button

Limit number of jobs created within a pipeline

• When a pipeline exceeds this limit, drop pipeline, do not create any jobs within it

Meta issue: https://gitlab.com/gitlab-org/gitlab-ee/issues/3477

/cc @bikebilly @ayufan @dimitrieh @DouweM