Logs Page: Add a new feature flag to switch environment logs page to vue

What does this MR do?

Creates a new feature flag:

Feature.enable('environment_logs_use_vue_ui')

To enable the new Vue based log page. This page will be empty before new features are added in upcoming MRs.

Background: This MR is an effort to split a big MR into separate pieces !18567 (merged).

Screenshots

FF on	FF off / before

Logs page will show empty for now.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• 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

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

Relates to #33537 (closed)