Improve the ssh-askpass.sh script

[vinokurig]

What does this PR do?

Do the default vscode flow (get the passphrase from the inputbox) under next conditions:

• If the passphrase file is missing.
• If the passphrase is incorrect, for that we test the passphrase with the ssh-keygen.

What issues does this PR fix?

fixes eclipse-che/che#23244

How to test this PR?

see eclipse-che/che#23244

Does this PR contain changes that override default upstream Code-OSS behavior?

• the PR contains changes in the code folder (you can skip it if your changes are placed in a che extension )
• the corresponding items were added to the CHANGELOG.md file
• rules for automatic git rebase were added to the .rebase folder

[github-actions]

Click here to review and test in web IDE:

[github-actions]

Pull Request images published ✨

Editor: quay.io/che-incubator-pull-requests/che-code:pr-453-amd64
Dev image: quay.io/che-incubator-pull-requests/che-code-dev:pr-453-dev-amd64

[RomanNikitenko]

Tested, with the PR changes system asks me to put a passphrase to confirm a git operation (I didn't provide a passphrase on the dashboard):

[vitaliy-guliy]

I'm not able to start a workspace after adding the key pair to my account via User Preferences -> SSH keys

Tested on the dogfooding with and without changes provided by this PR.

[vinokurig]

@vitaliy-guliy
If the issue is reproduced with default editor image, then it is not related to the pull request, could you please create an issue for that?

[devspacesbuild]

Build 3.18 :: code_3.x/1500: Console, Changes, Git Data