Introduce retention policy banner

What does this MR do and why?

Introduce retention policy alert

Add this informative message to all vulnerability reports to announce the upcoming feature in 18.0 that will archive vulnerabilities after a year.

Changelog: added EE: true

Note

• This MR does not add the dismissable functionality. I'll add it as a follow up to keep the MR size a bit smaller. It's also good as this is an important banner and we don't want it to be dismissed by mistake.
• I'll add a Learn More button as soon as the documentation page is ready. The note already contains details so this shouldn't be an issue
• This banner is going to be displayed only on gitlab.com

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

Apply the following diff:

diff --git a/ee/app/assets/javascripts/security_dashboard/vulnerability_report_init.js b/ee/app/assets/javascripts/security_dashboard/vulnerability_report_init.js
index fdb87f5a98ab..82021ad7ad6d 100644
--- a/ee/app/assets/javascripts/security_dashboard/vulnerability_report_init.js
+++ b/ee/app/assets/javascripts/security_dashboard/vulnerability_report_init.js
@@ -110,7 +110,7 @@ export default (el, dashboardType) => {
     groupFullPath,
     projectFullPath,
     vulnerabilityQuota,
-    showRetentionAlert: parseBoolean(showRetentionAlert),
+    showRetentionAlert: parseBoolean(showRetentionAlert) || true,
     fullPath: projectFullPath || groupFullPath,
     canAdminVulnerability: parseBoolean(canAdminVulnerability),
     hasVulnerabilities: parseBoolean(hasVulnerabilities),

and visit all these vulnerability reports to visualize the alert:

• Instance level /-/security/vulnerabilities
• Group level /groups/<group-name>/-/security/vulnerabilities
• Project level /<namespace>/<project-name>/-/security/vulnerability_report

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #524613 (closed)