chore: Allow a runtime test engine to start a nested instance

[dr1rrb]

Feature

Allow a runtime-test runner to start a nested instance
This allow a runtime-test runner running on a CI to start a new instance for hot-reload tests

What is the current behavior?

The CI fails to start a second app as some environnement variables are already set

What is the new behavior?

We only update environnement variables, never try to add it!

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Wasm UI Tests are not showing unexpected any differences. Validate PR Screenshots Compare Test Run results.
• Contains NO breaking changes
• Updated the Release Notes
• Associated with an issue (GitHub or internal)