Always display artifacts dropdown

Ref: #329798 (closed)

What does this MR do?

This MR stop exposing our has_downloadable_artifacts attribute from our pipelines.json API.

It also get rid of some custom javascript logic to determine when we need to display our download button as we always want to display it.

Why are we doing this?

Following up the work in #324003 (closed) where we started to lazy load downloadable artifacts once a user click on it as you can see below 👇

We continue to improve the ~performance of the index pipeline page, by cleaning up unnecessary data exposed by our API:

1. First step is to get rid of this data we no longer use in the frontend
2. Next step will be to remove those artifacts from being loaded on the pipeline page. This will be done in a follow up MR.

Screenshots

Does this MR meet the acceptance criteria?

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