Improve issues metric names in Value Streams Dashboard

What does this MR do and why?

For consistency, improve the issues metric names in Value Streams Dashboard

• Rename 'New issues' to 'Issues created'
• Rename 'Closed issues' to 'Issues closed'

Screenshots or screen recordings

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

• Visit the Value Streams Dashboard for any group (ex. http://gdk.test/groups/flightjs/-/analytics/dashboards/value_streams_dashboard)
• Verify the presence of Issues created and Issues closed

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #424223 (closed)