refactor: update username suggestions logic (#27525)
refactor: update username suggestions logic (#27525)

Used integers instead of alphanumerics to generate username suggestions.

VAN-52
arbrandes/edx-platform,angelapper/edx-platform,arbrandes/edx-platform,eduNEXT/edx-platform,eduNEXT/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,edx/edx-platform,arbrandes/edx-platform,edx/edx-platform,angelapper/edx-platform,arbrandes/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,edx/edx-platform,edx/edx-platform