Add byte count on the provider side

[vkuznecovas]

Make sure that byte counts are emitted for ongoing sessions.

[zolia]

We will need to update consumer side too since we will need configurable reporting frequency. Initially we might assume that reporting every 3 sec. should be enough. Given that payment invoicing frequency is 60 sec. atm. this should yield around 5% discrepancy.

[zolia]

Most likely we will need to address this bug too: #1674

[tadaskay]

We will need to update consumer side too since we will need configurable reporting frequency

I suggest opening a separate issue for that