Validate primary validator fee for signed change request

[dmugtasimov]

TODO:

• When primary validator receives a signed change request it must validate that it is being enough fee

[dmugtasimov]

@buckyroberts how should we maintain PV fees? Do they just declare whatever fee they want similar to node fees? This may lead to PV fees getting superhigh uncontrolled

[dmugtasimov]

This is bounty task, but it can't be pick until the description is fully described and a bounty assigned