Pipeline deletion from UI

Problem to solve

When deleting pipelines is possible from the API, it is not yet really accessible to any user from the UI.

Further details

Follow up from https://gitlab.com/gitlab-org/gitlab-ce/issues/41875 (enables deleting using the API)

Proposal

Make it possible to delete pipelines from the UI, instead of only through API

• Single delete mode (pipeline detail view) => !21365 (merged)
• Bulk selection mode (pipeline list view) => #196512 (closed)

What does success look like, and how can we measure that?

Users are able to delete pipeline entities from the UI, similar to how this is defined for the API in gitlab-ce#41875

Links / references

Edit from @marcel.amirault: To raise visibility, this is being worked on by @fh1ch in !21365 (merged)