Introduce share.user option in order to control samba option

[tobias-richter]

Hi @bertvv I just started to use your role (thanks for that) but i noticed that there is no support for force user, so I implemented it.

[darkiop]

hello @bertvv, thanks for this amazing role! I also have the requirement to use force user in the smb.conf. manually added to smb.conf.j2, as implemented by tobias here, that works too. is it possible to include this in your version? or is there another possibility that I have overlooked? thx and regards, Thorsten