Display new Web IDE callout in Web IDE button

What does this MR do and why?

Displays a user callout encouraging the user to try out the new Web IDE. The callout follows these rules:

• It doesn’t appear for editing single files.
• It is dismissed when clicking the "Web IDE" button.
• The user can also dismiss the callout by clicking the close button.

Screenshots or screen recordings

How to set up and validate locally

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

1. Enable the vscode_web_ide feature flag in your local environment by following these instructions:
   1. Run rails c in your terminal
   2. Once the rails terminal is running, execute Feature.enable(:vscode_web_ide)
2. Open the project overview or the project’s repository page. You will see the user callout in the Web IDE button.
3. If you close the callout, you can reset its state by running rails c again and executing the following command: Users::Callout.find_by(feature_name: "vscode_web_ide").delete()

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 #370139 (closed)