Don't force port 22 for rsync backup

[SoMuchForSubtlety]

Currently, the backup script has port 22 hardcoded. https://github.com/mail-in-a-box/mailinabox/blob/3a7de051ee1e87d08589a946e3d05bbf6f6806fc/management/backup.py#L19

This prevents setting a non-standard port via ~/.ssh/config and I don't see any upsides since port 22 is the default anyway.

I need to use port 23 since that is what's being used by hetzner storage box.

[ddavness]

I have this implemented on a fork of mine - if anyone wants to make a PR you can start by cherry-picking this commit: https://github.com/ddavness/power-mailinabox/commit/8a0805dae854ad6a5e13c2b1fe55b9a28490ff0e

[JoshData]

Yeah I can't think of a reason why -p 22 should be there, and I would accept a pull request removing it.

[schlypel]

@SoMuchForSubtlety this is merged in 61 and works now, can this be closed? Thanks.