Include flag to set different permissions during s3invsync transfer

[aaronkanzer]

Permissions set on files that were transfers were not optimal for read-only access across groups.

During our s3invsync transfer, files copied over to MIT Engaging had a default permissions of:

File-level:

-rw-------+

Directory Level

drwxrws---+

When first ssh'd onto a login node, output of umask is 0002; however, these permissions do not match such an setting that you'd expect from the default umask value.

The ideal permissions for our group are:

File-level

-rw-r-----+

Directory-level

drwxrws---+ (which was appropriate from the initial copy)

This GitHub issue captures the need to perhaps set temporary permissions that enable read-only access across groups/users for not just the user that transfers the files, but also others.

Perhaps a quick setting of umask 027, etc. could work here -- rather integrate something into s3invsync though upstream -- thanks all

Cc @kabilar @yarikoptic @satra @jwodder

[aaronkanzer]

A mini-update here -- chmod g+rs . was what I applied retroactively to the appropriate dirs. across Engaging -- it worked but was a bit of hassle due to the file count and size across the assets

Cc @satra @kabilar