add namespace-update-function-price as a function to @stacks/bns

[bilalanees98]

The namespace-update-function-price smart-contract fn should be provided as a function in stacks/bns. All other public namespace functions are provided in stacks/bns.

Not sure if this was left out intentionally or by mistake. But it'd be great to get some insight on this.

[smcclellan]

Thank you for this ticket! Would you be interested in submitting a PR for this? It may be implemented quicker if so. Otherwise, we will prioritize it and get to it later.

[bilalanees98]

I'll try to take out some time next week for this.