feat: support an identity file in CLI for ssh authentication (platform#91)

Description

Support an identity file in CLI for ssh authentication.

Use an identity key if specified, otherwise use an ssh-agent

Related issue

platform#91

Examples

Checklist

• the MR description has been reviewed
• this MR contains text changes and they have been reviewed OR there are no texts changes
• this MR contains GUI/CLI changes and they have been reviewed OR there are no GUI/CLI changes
• this MR contains API changes, specifications reflect those changes and they have been reviewed OR there are no API changes

Closes #91 (closed)