Remove banner from pipelines page

What does this MR do?

Result of a meeting with Kamil, Jacob, Sarrah, Dimitrie and Fabio:

• Remove all banners as they are now,
• Add an unobtrusive banner in Project page when the page is not empty,
• Add a context text in Project empty page

Screenshots (if relevant)

empty project	banner

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/38641 Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/39051 Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/38827 https://gitlab.com/gitlab-org/gitlab-ce/issues/38931