[docker] Copy files into container as user
[docker] Copy files into container as user

We use some scripts within the container as dev user. Explicitly copy
them as this user to ensure the user executing the script has
permissions on them later on.

(`COPY` always uses root:root as target user/group. On some machines,
the files ended up executable as docker ran, while on others it didn't.
Making things explicit should give us a consistent build experience.)

See #8569

Signed-off-by: Philipp Wagner <5a4b10454c30419e54a1570be358a516ff84bb63@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan