Docs: Additional docs for new VSA layout

What does this MR do?

Adds documentation for additional edit features in the new VSA layout:

• Hiding / removing / adding stages
• Customizing a value stream name
• Updates the example of a "Label based stage"

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have added/updated documentation, or it's not needed. (Is documentation required?
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Related to #323984 (closed)