mark namespace with label openfaas=1 valid

Description

faasd implementation was no allowing to deploy functions into namespace with label openfaas=1. Instead code was written to validate openfaas=true.

Motivation and Context

[x] I have raised an issue to propose this change this is required Closes #351

How Has This Been Tested?

Create and install a local build of faasd binary using make local
Run the below script to deploy functions with label openfaas=1. Script is using go-sdk which includes label openfaas=1 for any new namespace created.
```
package main
```

import ( "context" "fmt" "log" "net/http" "net/url" "os" "time"

"github.com/openfaas/faas-provider/types"
"github.com/openfaas/go-sdk"

)

func main() { username := os.Getenv("OPENFAAS_USERNAME") password := os.Getenv("OPENFAAS_PASSWORD")

gatewayURL, _ := url.Parse(os.Getenv("OPENFAAS_GATEWAY_URL"))
auth := &sdk.BasicAuth{
    Username: username,
    Password: password,
}
nsName := "test-sdk-ns"
fnName := "env-store-test"

client := sdk.NewClient(gatewayURL, auth, http.DefaultClient)

// create namespace
_, err := client.CreateNamespace(context.Background(), types.FunctionNamespace{
    Name: nsName,
    Labels: map[string]string{
        "purpose": "test",
    },
})

if err != nil {
    log.Fatalf("Namespace creation Failed: %s\n", err)
}
fmt.Printf("Namespace %s created!\n", nsName)

// get namespace
res, err := client.GetNamespace(context.Background(), nsName)

if err != nil {
    log.Fatalf("Namespace get Failed: %s\n", err)
}

fmt.Printf("GetNamespace: %q\n", res)

// update namespace
_, err = client.UpdateNamespace(context.Background(), types.FunctionNamespace{
    Name: nsName,
    Labels: map[string]string{
        "purpose": "test",
        "demo":    "false",
    },
    Annotations: map[string]string{
        "anno": "true",
    },
})

if err != nil {
    log.Fatalf("Namespace update Failed: %s\n", err)
}

res, err = client.GetNamespace(context.Background(), nsName)

if err != nil {
    log.Fatalf("Namespace get Failed: %s\n", err)
}

demo, found := res.Labels["demo"]

if !found || demo != "false" {
    log.Fatalf("Namespace update Failed: %s\n", err)
}
fmt.Printf("Updated Namespace: %q\n", res)

// get namespaces
namespaces, err := client.GetNamespaces(context.Background())
fmt.Printf("Namespaces: %q\n", namespaces)

// deploy
_, err = client.Deploy(context.Background(), types.FunctionDeployment{
    Service:    fnName,
    Image:      "ghcr.io/openfaas/alpine:latest",
    Namespace:  nsName,
    EnvProcess: "env",
})

if err != nil {
    log.Fatalf("Deploy Failed: %s\n", err)
}
fmt.Printf("Deploy Completed!\n")

fmt.Printf("Sleep....\n")
time.Sleep(15 * time.Second)
fmt.Printf("Sleep Finish\n")

fn, err := client.GetFunction(context.Background(), fnName, nsName)
fmt.Printf("Function: %v\n", fn)
if err != nil {
    log.Fatalf("GetFunction Failed: %s\n", err)
}

// fmt.Println("Scale to Zero")
// err = client.ScaleFunction(context.Background(), fnName, nsName, 0)
// if err != nil {
//  log.Fatalf("ScaleFunction Failed: %s\n", err)
// }

// fmt.Printf("Sleep....\n")
// time.Sleep(15 * time.Second)
// fmt.Printf("Sleep Finish\n\n\n\n")

// // delete
// err = client.DeleteFunction(context.Background(), fnName, nsName)
// if err != nil {
//  log.Fatalf("DeleteFunction Failed: %s\n", err)
// }
// fmt.Print("Function Deleted!\n\n\n\n")

// // delete namespace
// err = client.DeleteNamespace(context.Background(), nsName)
// if err != nil {
//  log.Fatalf("Namespace %s delete Failed: %s\n", nsName, err)
// }
// fmt.Printf("Namespace %s deleted!\n\n\n\n", nsName)

}

3. Below output was produced for the above script

Namespace test-sdk-ns created! GetNamespace: {"test-sdk-ns" map[] map["openfaas":"1" "purpose":"test"]} Updated Namespace: {"test-sdk-ns" map[] map["demo":"false" "openfaas":"1" "purpose":"test"]} Namespaces: ["openfaas-fn" "test-sdk-ns"] Deploy Completed! Sleep.... Sleep Finish Function: {env-store-test ghcr.io/openfaas/alpine:latest test-sdk-ns env map[] [] [] 0xc000014228 0xc000014230 false 0 1 1 2023-11-28 20:50:06.077724974 +0000 UTC }



## Types of changes
<!--- What types of changes does your code introduce? Put an `x` in all the boxes that apply: -->
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

## Checklist:

Commits:

- [x] I've read the [CONTRIBUTION](https://github.com/openfaas/faas/blob/master/CONTRIBUTING.md) guide
- [x] My commit message has a body and describe how this was tested and why it is required.
- [x] I have signed-off my commits with `git commit -s` for the Developer Certificate of Origin (DCO)

Code:

- [x] My code follows the code style of this project.
- [ ] I have added tests to cover my changes.

Docs:

- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.

openfaas / faasd