Implement customization provider for operation approval

[petrdvorak]

Currently, the customer implementations have no means of customizing operation approval logic. We should implement additional customization provider interface that would act allow modifying behavior whenever:

• Downloading the operation list
• Approving the operation

Example use-cases:

• Do not allow operation approval for activations with insecure flags.
• Do not allow operation approval using applications with insufficient role set.
• Log information about certain approved operation to a custom system, i.e., an incident managnement.