fix for local file uploads without scheme

[d-vignesh]

Fix issue on scenario where local file path is provided without scheme in add_external_file functionality.

Related Issue \ discussion

Fix for #1313

Patch Description

If the file added has a local path, the absolute path is fetched and the 'file://' scheme is added.

Testing Instructions

Described in [#1313]

Other Information

Tested file addition using absolute path, relative path and remote path. File addition and upload is working fine. I could only test for Windows system.