pmb.config.init: copy pmaports githooks to default git hooks dir

So that githooks can be used in pmaports without the risk that symlinks
pose when checking out random branches from random people. The hooks
are copied, only when doing "pmbootstrap init", selecting the edge
channel and having the master branch checked out (not any other branch
on the edge channel or on any other channel).

Closes: pmaports#2055
Related: pmaports!4008
Signed-off-by: Pablo Correa Gómez <ablocorrea@hotmail.com>
Reviewed-by: Oliver Smith <ollieparanoid@postmarketos.org>
Reviewed-by: Clayton Craft <clayton@craftyguy.net>
Co-developed-by: Oliver Smith <ollieparanoid@postmarketos.org>
Link: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/%3CDB9P192MB129107CAA025F4EF59D3FB53C7999@DB9P192MB1291.EURP192.PROD.OUTLOOK.COM%3E