feat: allow set global dns servers from client plugin config for contains

[ttys3]

so we can config dns for containers like:

plugin "nomad-driver-podman" {
  config {
     dns_servers = ["192.168.8.100"]
  }
}

[jdoss]

Why would you want to set this in the plugin section of the nomad config when you can just set DNS via https://developer.hashicorp.com/nomad/docs/job-specification/network#dns-1 in the networking block of the job?

[ttys3]

Why would you want to set this in the plugin section of the nomad config when you can just set DNS via https://developer.hashicorp.com/nomad/docs/job-specification/network#dns-1 in the networking block of the job?

Do you think I am unaware of this configuration option? No, I am not.
When I submitted this PR, I had already been using this solution for almost two years.
The issue is that this DNS configuration must be global; I do not need to set different DNS for different services. Additionally, I do not want containers to directly use the upstream gateway's DNS because I want to use Consul DNS for service resolution. It is clearly not practical to configure DNS for each task within each job.

the arch is:

                                 +-----------------+
                                 |  Nomad Cluster  |
                                 +-----------------+
                                        |
                                        |
                                        |
                                        v
                           +------------------------+
                           |                        |
                           |  app deployed via      |
                           |  nomad cluster         |
                           |                        |
                           +------------------------+
                                        |
                                        |
                                        |
   +------------------------+           v                  
   |                        |   +-----------------+        
   |   Container App        |<--+ Consul Catalog  |        
   |                        |   +-----------------+        
   | Query DNS via Consul   |                              
   +------------------------+                              
                                        |                  
                                        |                  
                                        |                  
                                        v                  
                                +---------------+          
                                |               |          
                                |   Consul DNS  |          
                                |               |          
                                +---------------+          
                                        |                  
                                        |                  
                                        |                  
                                        v                  
                                +---------------+          
                                |               |          
                                |  DNS Response |          
                                |               |          
                                +---------------+          

yes, I also have CNI network and uses flannel network fabric, so different nomad node machine can commuicate with each other via the cluster network.

[shoenig]

needs to be go-fmt'd

[shoenig]

The docker task driver also already has a dns_servers config option; it would make sense to make it available for podman too.

[shoenig]

Also @ttys3 if you don't mind rebasing on main; there's some CI fixes in there to help getting tests working again.

[jdoss]

Do you think I am unaware of this configuration option? No, I am not. When I submitted this PR, I had already been using this solution for almost two years.

No need to get defensive. Your original PR had zero details on why this was needed and I was simply asking to better understand your use-case and the reason for the PR. Thank you for taking the time to explain why. I appreciate it.

[ttys3]

Do you think I am unaware of this configuration option? No, I am not. When I submitted this PR, I had already been using this solution for almost two years.

No need to get defensive. Your original PR had zero details on why this was needed and I was simply asking to better understand your use-case and the reason for the PR. Thank you for taking the time to explain why. I appreciate it.

Sorry my previous reply was a bit unkind. I take back what I said before.

[ttys3]

Also @ttys3 if you don't mind rebasing on main; there's some CI fixes in there to help getting tests working again.

@shoenig rebased and formated, PTAL

[shoenig]

LGTM; thanks @ttys3!