bustash-put: Add flag to build index from ingested .tar stream

[nh2]

I have some existing bustash backups that I'd like to re-write, to delete some large temp directories that were accidentally included in the backups.

There is currently no command to that.

I also cannot us

bupstash get | bupstash put

and apply some filtering on the tar stream in the middle, because as described under TIPS that would disable the ability to

create a snapshot listing for other commands like bupstash-list-contents

which I need.

So my feature request: That this snapshot listing can be added for any bupstash-put, constructing it on the fly from the tar stream.

[andrewchambers]

I believe this is technically possible but wasn't added because the ingested tarball has some file ordering requirements that normal tar tools wouldn't adhere to. I don't have any ETA on this feature but I agree it would be very useful.