Avoid overriding existing Changie config file if already exists

[miniscruff]

Discussed in #403

^{Originally posted by llaville November 12, 2022}
With Changie v1.10.0

When you have a .changie.yaml file in your repository and run the changie init command, the default version of .changie.yaml override the current existing version.

Consider either to :

1. add an option to avoid this behavior
2. display a warning message
3. changie init write a .changie.yaml.dist file instead

PS: It's same for .changes/ folder and header template file

Plan

1. If a .changie.yaml file exists, do nothing and exit(1) a helpful message
2. Add a --force option to init to skip the check above for those living on the edge.