Job to mark Organization of GitLab employees

Summary

As observed in !27045 (comment 308209218), it can so happen that the Organization field of a GitLab employee is out of sync. Meaning, a user can have their email domain as gitlab.com, and the organization could be set to something other than GitLab.

This issue is to ensure that we run a job (maybe just once) to mark the Organization of all GitLab employees as GitLab.

Also, for new users - add a after create a hook to automatically set Organization as 'GitLab', if the user is a GitLab employee.

Steps to reproduce

(How one can reproduce the issue - this is very important)

Example Project

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(If you are using an older version of GitLab, this will also determine whether the bug is fixed in a more recent version)

What is the current bug behavior?

(What actually happens)

What is the expected correct behavior?

(What you should see instead)

Relevant logs and/or screenshots

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Output of checks

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Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)