add modified date to sftp file list

Description

I added the modified datetime of the files when viewed in the SFTP window. I relied on the mtime file attribute extracted using libssh. The format I opted for is "2022-08-02 00:15:00" which I believe is the simplest to sort as a string.

Related Issue

Motivation and Context

Working with sftp to access remote servers, I often need to download the latest files such as logs or application generated files. I believe adding the modified date as practiced by other ftp/sftp GUI tools helps a lot.

How Has This Been Tested?

I tested by accessing a remote Debian 10 Linux server via SFTP, then listing the contents of the home folder. The modified time of the files was correct and I could also sort by that column. I ran Remmina on my Laptop which is running the latest Manjaro (Arch-based) distribution.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.