Content directory imposed CRT constraints

# Background
One of the main issues with CRTs on DeSo was lack of long term alignment between issuer and buyers. Unfortunately for them, they did not have vesting, which we do, but we can do even better: governance.

# Proposal
Allow lead, or council, to set global constraints on CRTs that can be issued, e.g.

* max daily number
* only channels that are verified (is this in state?) and/or some how at a given tier (permission levele?)
* min vesting schedule for issuer
* whether permission less demonstrability is ok
* max patronage
* etc.

This is not a spec, it's an idea, implementer should come up with concrete design before starting.

Probably also constraints on [sale terms](https://github.com/Joystream/joystream/issues/2362#issuecomment-1059012676) and other parameters is also sensible. Implementer should provide exhaustive list of constraints.

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