Add support for setting mode of a container content mount

[troglobit]

Description

When mounting content into a file in a container, the resulting file in the container inherits the file mode from the source. This is usually not sufficient, in particular in the case of /etc/rc.local, which needs to be executable.

Alternatives:

1. At least, add a file mode setting to the YANG model
2. Infer defaults from the destination file, by "fishing out" the file from the image

Additional Information

If we can infer from the image we could also use this to infer the contents as well.

General Information

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Please use this issue for discussions related to the feature.