add support for stateless rules

[robo-cap]

Add option to create NSGs with stateless rules.

[hyder]

Can you please elaborate why:

1. we need stateless rules here
   2)all rules need to be stateless?

[robo-cap]

Can you please elaborate why:

1. we need stateless rules here
   2)all rules need to be stateless?

1. With this PR I want to provide the option to choose between stateful and stateless rules via the use_stateless_rules variable.
2. Stateless rules will be used by default for the ease of setup and troubleshooting.
3. Egress rules to 0.0.0.0/0 from pods and worker nodes will be stateful independent of the value for use_stateless_rules variable because of security concerns.
4. It's recommended to use stateless rules for large clusters.
5. I strongly recommend for stateless rules setup to be tested before using it in production. This is why for now it is considered EXPERIMENTAL.