Add link to forecast feedback issue at top of Deployment Frequency page

What does this MR do and why?

Displays info alert with link to forecast feedback issue at the top of the Deployment Frequency page when Trend Forecasting feature is toggled on.

Screenshots or screen recordings

Before	After
Screen Recording 2023-07-21 at 4.42.18 PM.mov	Screen Recording 2023-07-21 at 4.41.06 PM.mov

How to set up and validate locally

1. Feature.enable(:dora_charts_forecast, GROUP_ID)
2. Go to http://{local-instance}/groups/gitlab-org/-/analytics/ci_cd?tab=deployment-frequency
3. Click toggle

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 #416834 (closed)