Support for environment variables during workspace creation

Issue: Provide environment variables during workspace ... (#463514 - closed)

What does this MR do and why?

Support for environment variables during workspace creation.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Context	Screenshot
Workspace creation default state
When a new variable is added
When a validations fail on submit

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Browse http://gdk.test:3000/-/remote_development/workspaces/new .
2. Select a project and cluster agent.
3. Click on Add Variable button. Fill in the key value pair.
4. Click on Create Workspace.
5. Once workspace URL becomes available, click on it which will open the IDE.
6. Open up a terminal in the IDE and run the command env and verify that the variable you provided during creation is available here.