[Feature] Support for logs in namespaces

The faas-netes provider along with the SDK has a way in which you can specify namespaces for log requests. The namespaces support should be added for the logs.

Expected Behaviour

Check logs of figlet in dev namespace:

faas-cli logs figlet --namespace dev

faas-cli logs figlet.dev

And one of the commands should succeed.

Current Behaviour

Logs does not support this feature

Possible Solution

Imaplement --namespace flag in logs see list for example

Steps to Reproduce (for bugs)

Try logs in dev namespace faas-cli logs figlet --namespace dev
Check:
```
Unknown flag: --namespace
```
Try by naming convention faas-cli logs figlet.dev

Check:

WARNING! Communication is not secure, please consider using HTTPS. Letsencrypt.org offers free SSL/TLS certificates.
Handling connection for 8080
Server returned unexpected status code: 500 - unknown log request error (500)

Context

Logs on the server side now support namespaces, the client should follow.

Your Environment

FaaS-CLI version ( Full output from: faas-cli version ): Latest
Docker version ( Full output from: docker version ): 18.04
Are you using Docker Swarm (FaaS-swarm ) or Kubernetes (FaaS-netes)? Kubernetes
Operating System and version (e.g. Linux, Windows, MacOS): N/A
Link to your project or a code example to reproduce issue: Check Steps to Reproduce

openfaas / faas-cli