Define a pattern for adding/showing/removing multiple items

We currently have a lot of different patterns in place for showing data when the user can add multiple items.

Some examples:

Streamed Audit Events (headers)

New Pipeline

Webhooks settings

Status checks settings

Branch protection settings

Deploy tokens settings

MR settings

Differences

• Different table styles
• Some use just a list style
• Remove button
• Add button / Auto adding new line
• Some have a disabled add button when form is empty