Add mode property for restricting file upload access

[gboyvalenkov-bosch]

Currently, with the dynamic configuration of uploaded files, all files readable by the upload executable can be uploaded to the cloud. This may be undesirable and unexpected behavior.

To give more control and transparency over what can be uploaded, add a mode configuration property, with the following options:

• strict - upload is permitted only for the files specified with the files configuration property (i.e. the dynamic upload files configuration is disabled).
• lax - no restrictions on dynamic upload (i.e. any files can be requested with the dynamic file property).
• scoped - must be used in conjunction with the files property. Allows upload only of files matching the files glob pattern

The default mode is strict. If an attempt is made to start the upload executable, without providing the files property, it should exit with an error. The error should make it clear, that if dynamic upload is desired, the mode property should be set to lax.