Use gitlab_web_url in issuable.vue

What does this MR do?

A previous MR introduced gitlab_web_url to Jira issues. We handled this in app/assets/javascripts/issuable_list/components/issuable_item.vue (!53804 (diffs)), but we also must handle it in app/assets/javascripts/issues_list/components/issuable.vue.

Each of these components is currently toggled in and out via the :jira_issues_list feature flag. The feature flag is currently disabled by default, and for this state, app/assets/javascripts/issues_list/components/issuable.vue is used.

Related issue: #322556 (closed), #298724 (comment 515570865)

Screenshots (strongly suggested)

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