Resolve "Monitoring graph axes labels are inaccurate and inconsistent"

What does this MR do?

• fixes the x-axis scaling by accounting for the transform offset
• adds a stroke to the x-axis hash marks to make them visible
• tidy up some code

Screenshots (if relevant)

Before:

(note the x-axis scale does not match the timestamp in the mouseover flag)

After:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• 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 #37105 (closed)