Add validity_checks_enabled backend-to-frontend data flow

What does this MR do and why?

Currently the behaviour when the user is opted-out of Validity Checks is to display the default value of Possibly Active Secret. This is confusing as it might give the impression that the worker is still running even when it shouldn't be. This MR will hide the Token Status field when user is not opted in.

Add validity_checks_enabled backend-to-frontend data flow

• Send validity_checks_enabled from backend to frontend via helper
• Enable conditional rendering of Validity Check features based on user opt-in
• Add comprehensive test coverage for validity_checks_enabled functionality
• Update vulnerability details component to consume validity checks state

Allows the frontend to conditionally display Validity Check related UI elements only when users have explicitly enabled the feature.

Changelog: changed EE: true

References

[FE] Hide Validity Token Status When Opt-in is off (#551812 - closed) • Radu Birsan • 18.2

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. in rails console enable the feature flag

 Feature.enable(:validity_checks)

2. Navigate to project then Secure > Security Configuration
3. Scroll down to Pipeline Secret Detection and enable it but make sure Validity Checks toggle is OFF
4. Add a secret to your project and ensure the pipeline runs
5. Check Secure > Vulnerability Report for the generated entry and ensure Token Status section doesn't appear

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