Merge branch 'dz/383238-update-preview-billable-users-API' into 'master'

Add willIncreaseOverage to billableUserChange

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/105355



Merged-by: Jannik Lehmann <jlehmann@gitlab.com>
Approved-by: Ryan Cobb <rcobb@gitlab.com>
Approved-by: Edgars Bralitis <ebralitis@gitlab.com>
Approved-by: Angelo Gulina <agulina@gitlab.com>
Approved-by: Jannik Lehmann <jlehmann@gitlab.com>
Co-authored-by: dzubova <dzubova@gitlab.com>