[BUG] KustomizeGenerator: order of the output of the `listFiles` template function is not stable

[cbarbian-sap]

Describe the bug
The order of the slice returned by the listFiles template function is not stable.

Tested with Version
v0.3.91

To Reproduce
Steps to reproduce the behavior:

1. Render the result of listFiles into the datapart of a config map.
2. Observe that it fluctuates when reconciling it some times.

Expected behavior
The result should be stable (e.g. alphabetically sorted)