add cloud provider flag for create namespace

[jumbogo]

What was changed

Add cloud provider flag to tcld namespace creation, so we can support multiple cloud. gcp example:

./tcld --server "saas-api.tmprl-test.cloud:443" n c --cf cert.pem --region us-central1 --namespace zz-test-tcld-ns-gcp-2 --cloud-provider=gcp

Why?

Checklist

1. Closes

2. How was this tested:

3. Any docs updates needed?