Allow changing the path that oasis uses for ssb stuff (i.e. normally ~/.ssb/)

[Powersource]

What's the problem you want solved?

When developing oasis you often want to e.g. publish messages just to test that things are working a certain way, but you don't want those test messages to end up in your normal profile/network. E.g. @lindskog is working on #537 right now and is posting fruit to see how the bug works/if it's fixed (not calling her out :P , I'd do it too).

Is there a solution you'd like to recommend?

Adding (if it doesn't exist) and documenting a command line option --path that sets where to store ssb related files.

I think I read some time ago that this was possible but I can't find it documented anywhere. Either way patchwork has this flag and that helped me while I was working on the peer invites PR, it let me make a new profile on the same machine that I could then try inviting.