T98: [sftp] Add support for posix-rename@openssh.com
### Description
**Originally reported by asn: https://bugs.libssh.org/T98 **
We should add support for posix-rename@openssh.com which supports renaming with atomic posix semantics.
sftp_rename() should use this extension by default if the sftp supports it.
### Comments:
**Jakuje commented on 2018-10-09 12:51:04 UTC:**
This landed in 6c56c1e0d72670da274f3e77c51a7b4e078d59c6
But it is not yet supported in client (`sftp_rename()`) by default.
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**asn commented on 2018-10-09 12:55:38 UTC:**
We need it on the client side in sftp_rename()
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issue