Change organization field to `readonly` for GitLab employees

What does this MR do?

See #207118 (closed)

Original MR before scope changed: !27045 (closed)

backend counterpart issue and MR: #209327 (closed) !26836 (merged)

For users with a @gitlab.com email address (See !26836 (merged) for how this is being determined):

• On edit profile page it changes "Organization" field to readonly and pre-populates with "GitLab"

Local Testing

1. Enable :gitlab_employee_badge feature flag.
   • bin/rails console
   • Feature.enable(:gitlab_employee_badge)
2. In lib/gitlab.rb change self.com? to return true
3. Create a user with a @gitlab.com email address
4. Navigate to /profile, Organization field should be readonly

Note: You may need to run gdk restart because of the caching on app/models/user.rb

Feature Flag

This MR is behind the :gitlab_employee_badge feature flag. Flag is used in app/views/profiles/show.html.haml.

Screenshots

Page	Before	After
Edit Profile

Followup Issues

Require @gitlab.com email to be verified

#212618 (closed)

Backfill Organization field of users with @gitlab.com email and prefill Organization field of new users with @gitlab.com email.

Issue: #212461 (closed)
Per this thread: !27045 (comment 308209218)

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