Rollout security navbar to more users

What does this MR do?

Rolls out security navbar to users created 2019-11-01 and onward

Issue #208264 (closed) and comment gitlab-org/growth/team-tasks#54 (comment 294922460)

Screenshots

@a_akgun lets bump the roll out to 50% of users created on or after 2019-11-01 this should give us enough eligible users for the experiment to run and deliver results in this quarter.

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