Fix environment variables GUI for new apps

[patzeltj]

Description

This pull request addresses a bug in the Stratos GUI that caused issues with displaying and managing environment variables for new applications in the GUI. The fix ensures that the environment variables object is not NULL and provides an empty object if necessary.

Motivation and Context

When a new app was created, the environment variables were not shown correctly. This was caused by a NULL entry. The entry prevented the GUI from displaying the environment variables correctly because it had nothing to iterate over. It also prevented the setting of new variables and prevented variables that were set manually from being shown. This was solved by inserting an empty object if the variable is currently set to NULL.

How Has This Been Tested?

This fix has been running on the STACKIT Stratos for two years. It was manually tested by creating a new application and testing that the env variables were shown correctly and were editable in the GUI.

Types of changes

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] Docs update
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [X] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [X] I have followed the guidelines in CONTRIBUTING.md, including the required formatting of the commit message

[wayneeseguin]

Straightforward change, great PR!