Fix ECR and DockerHub sync

What does this MR do?

The ECR sync script had a few problems like:

• The comma separated arguments weren't parsed properly
• The image generation was far from generating all the images needed to be synced
• The image generation turned out too complex

I did my best to find all the existing image variants and sync them while also verifying that with tests.

---

I also had to refactor the Go scripts structure in the scripts directory. I moved the packagecloud script to its own directory since no two scripts with a main package can exist in one directory and this is in-line with other scripts. Now the whole scripts directory uses one go.mod file so they share dependencies only with themselves.

Why was this MR needed?

To fix #34658 (closed) and #33917 (closed) and to enable image sync in the pipeline as I had to disable it during the last release.

What's the best way to test this MR?

What are the relevant issue numbers?

Closes #33917 (closed) #34658 (closed)