Generic ProviderConfig generation

[kasey]

Terraform gives us the schema of provider configuration fields which we can use to code generate a provider with initialization methods. Currently we are hard-coding these types and initialization methods. Since the pattern of having a username and password or token is fairly common, we could also have boilerplate config secret generation. The config yaml for the provider in /provider-configs/ could specify the names of fields in the secret which would be automatically mapped to the corresponding fields in the ProviderConfig -- these fields would also then be filtered out of the providerconfig spec.