Support for passphrase protected SSH keys

[vitaliy-guliy]

Describe the bug

SSH:Upload Private Key... command must upload a private key to your workspace and register it with ssh-add.

The command says that everything's OK, and the key is successfully uploaded.

But cloning the git repository using SSH link fails.

Che version

• nightly

Steps to reproduce

1. Generate SSH key on your local machine, enter passphrase when asked.

ssh-keygen -t ed25519 -C "your_email@example.com"

2. Add generated public key to your GitHub account

3. Go to Che-Theia, open command palette, find and run SSH: Upload Private Key...

4. Enter name for uploaded (it's just a label for uploaded fey, enter anything here)

5. Enter passphrase for your key, which you entered when generating the key

Che-Thea on this step will say that the key was successfully added.

6. Open a terminal in theia-ide container, go to /projects and clone any project with SSH URI
   e.g. git@github.com:eclipse/che-theia.git

Upload the file by hands:

• open a terminal in theia-ide. Remove all registered keys with ssh-add -D. If it says that Could not open a connection to your authentication agent., run the agent with ssh-add -D and try to remove keys again
• drag and drop the keyfile to explorer view
• change file permissions chmod 0600 keyfile
• register the file with ssh-add keyfile
• clone the repository again git clone git@github.com:eclipse/che-theia.git