Plugin download process must happen on a temporary file

[salehkhazaei]

Describe the bug
When downloading a plugin (e.g. updating plugin version) if for any reason plugin download breaks, the plugin binary will be corrupted.
Although config file wont take the effect until after download is completed, we need to make sure that we dont break the plugin binary.
It's better to download the new file into a temporary file and then move it on the plugin binary once download is finished.