fix: prevent popup disappearing

[vitaliy-guliy]

Adds a workaround to prevent popup disappear.
An issue in the upstream describing the problem microsoft/vscode#214787

We should remove the code from activate() function in devfile-extension.ts file after fixing the upstream issue.

How to test:

• create a workspace using this repository and the editor quay.io/vgulyy/che-code:without-devfile-walkthrough-extension
• install node dependencies
• in a terminal run npm run watch
• Go to Run and Debug view and run the extension
• add few environment variables, etc.

[openshift-ci]

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This pull-request has been approved by: RomanNikitenko, vitaliy-guliy

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