Make cryptogen and configtxgen non-internal modules

### Current Status

Both cryptogen and configtxgen import internal go modules.
Meanwhile cmd/cryptogen and cmd/configtxgen seem tightly-encoupled to using yaml files. Using yaml files would result in decreased maintainability as the app scales up.
As there are some bits and pieces of the code in e.g., internal/cryptogen/ca, csp, msp, etc. that are useful for generating certificates, it would be nice to know the reasoning behind them being internal modules, or else would be nice to have them available publicly, such that we developers can make use of those functionalities more dynamically, without being constraint to either generating a yaml for the sake of generating crypto materials, or porting over the internal code to the project.

### Expected

Both cryptogen and configtxgen are capable of importing non-internal go modules available to public.

### Solution

Both cryptogen and configtxgen are capable of importing non-internal go modules available to public.

### Please let us know if you plan to work on this.

If the devs don't have specific time to make this refactoring change, I would love to if you would like me to contribute.