fix: take into account all existing files in given path when bootstraping

[dateutli]

Description:
Currently, when bootstrapping missing config files, a map of existing files is created so when clean up is performed we don't remove any existing ones. However, this line effectively makes it so only existing valid yaml files are considered for this map. If there were any other existing files this could lead to the accidental removal of those.

Testing:
Current behavior:

> mkdir testing
> touch testing/sample.txt
> touch testing/sample2    
> ls testing/ 
sample.txt sample2
> topicctl rebalance --cluster-config='examples/local-cluster/cluster.yaml' --path-prefix='testing' --bootstrap-missing-configs
[2026-03-13 13:45:25]  INFO --progress-interval is 0s. Not showing progress...
[2026-03-13 13:45:25]  INFO Getting all topic configs from path prefix testing
[2026-03-13 13:45:25]  INFO Rebalance complete! 0 topics rebalanced successfully, 0 topics had errors
> ls testing/

After fix:

> touch testing/sample.txt
> touch testing/sample2    
> ls testing/ 
sample.txt sample2
> topicctl rebalance --cluster-config='examples/local-cluster/cluster.yaml' --path-prefix='testing' --bootstrap-missing-configs
[2026-03-13 13:56:25]  INFO --progress-interval is 0s. Not showing progress...
[2026-03-13 13:56:25]  INFO Getting all topic configs from path prefix testing
[2026-03-13 13:56:25]  INFO Rebalance complete! 0 topics rebalanced successfully, 0 topics had errors
> ls testing/ 
sample     sample.txt