Move trials controller/view layer to gitlab_subscriptions module

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/166148



Merged-by: Miranda Fluharty <mfluharty@gitlab.com>
Approved-by: Jay Montal <jmontal@gitlab.com>
Approved-by: Pam Artiaga <partiaga@gitlab.com>
Approved-by: Fernanda Toledo <ftoledo@gitlab.com>
Approved-by: Tiffany Rea <trea@gitlab.com>
Approved-by: Miranda Fluharty <mfluharty@gitlab.com>
Reviewed-by: Doug Stull <dstull@gitlab.com>
Reviewed-by: Jay Montal <jmontal@gitlab.com>
Reviewed-by: Fernanda Toledo <ftoledo@gitlab.com>
Co-authored-by: Doug Stull <dstull@gitlab.com>