Create empty tabs and feature flag

What does this MR do and why?

create tabs for code flow (in vulnerability details page) with new feature flag called 'vulnerability_code_flow'

MR acceptance checklist

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

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Before	After

How to set up and validate locally

1. Upload a GitLab Ultimate license
2. Enable the feature flag (echo "Feature.enable(:vulnerability_code_flow)" | rails c)
3. Clone the code flow project and run his pipeline to display vulnerabilities
4. Navigate to the project => Secure => Vulnerability report => Select the first vulnerability to navigate to the vulnerability details page
5. Apply the following patch to show the new features

Patch

diff --git a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue
index ca4110274476..319e8f7180ae 100644
--- a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue
+++ b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue
@@ -56,6 +56,7 @@ export default {
       },
     },
     showCodeFlowTabs() {
+      return true
       return (
         this.glFeatures.vulnerabilityCodeFlow && !isEmpty(this.vulnerability.details.codeFlows)
       );
diff --git a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue
index bfbc47e4c041..72fd47398163 100644
--- a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue
+++ b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue
@@ -221,6 +221,7 @@ export default {
       return this.vulnerability.location?.file && this.vulnerability.location?.startLine;
     },
     showCodeFlowButton() {
+      return true
       return (
         this.glFeatures.vulnerabilityCodeFlow && !isEmpty(this.vulnerability.details.codeFlows)
       );

6. Verify the tabs appear and the user is directed to the Details tab
7. Verify the View code flow button appears
8. Verify clicking on the Code flow tab updates the url to include ?tab=code_flow
9. Verify clicking the View code flow button navigates the user to the Code flow tab

Related to #469653 (closed) and #458062