Move lengthy data attributes from view into helper

What does this MR do?

This MR is a follow-up to work done in !40304 (merged) and builds on the work done in !40657 (merged).

In !40657 (merged) some of the complex logic from the welcome view was moved into helper methods. This MR continues that trend by moving an additional piece, which is more lengthy than it is complex, from the view into a helper method. This also helps us clean up the view even more by removing the onboarding_issues_experiment_enabled variable from the top of the view file, as it is now only used internally by the extracted helper methods.

No changelog is necessary as this is a purely developer-facing change. Likewise, this change does not alter anything which requires updated documentation.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Slightly related to #240917 (closed) & !40504 (merged); depends on !40657 (merged)