Suppress update events on pipeline if already they got scheduled

What does this MR do?

Reduces the pressure on Sidekiq by queueing much less pipeline updates.

Why was this MR needed?

Currently we do queue updates on pipeline when we are processing a pipeline, this is very redundant as we don't really need to do this, because we do update pipeline status at the end of process.

The same applies to when we retry a build, we do queue updates on pipeline generated for all builds on next stages. This is completely redundant too.

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

None yet.