[FIX] project: make custom fields copiable again

Since #73341 copy_data is filtered to avoid leaking information to portal user.
Partically, it makes custom field not copiable.

Fix it by disabling the filter for internal users. This may lead to a problem
with hacky field `personal_stage_type_ids`. To avoid extra complexity in the
code, just mark it as `copy=False`. The latter change is kind of an improvement
from functional point of view, since using default personal stage seems to be a
better idea rather than copying the stage.

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opw-2746922

closes odoo/odoo#86757

Signed-off-by: Laurent Stukkens (ltu) <ltu@odoo.com>