Init Consul Client - Using k8s Service account

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#### Feature Description

I want to set up a Consul client by authenticating with my Kubernetes service account.

I don't understand at all why the `ACL().Login()` method doesn't update the Vault client with the Secret, and why I have to declare a new one using the newly created secret.

I suggest using the same authentication method as your other tools, including Vault.
#### Use Case(s)

```golang
package client

import (
"os"

"github.com/hashicorp/consul/api"
)

func newConsulClient() (*api.Client, error) {
consulConfig := newConfig()
client, err := api.NewClient(consulConfig)
if err != nil {
return nil, err
}

bearerToken, err := os.ReadFile("/var/run/secrets/kubernetes.io/serviceaccount/token")
if err != nil {
return nil, err
}
auth := &api.ACLLoginParams{
AuthMethod: "k8s",
BearerToken: string(bearerToken),
}
aclToken, _, err := client.ACL().Login(auth, nil)
if err != nil {
return nil, err
}

newConfig := newConfig()
newConfig.Token = aclToken.SecretID
client, err = api.NewClient(newConfig)
if err != nil {
return nil, err
}

return client, nil
}
```

Where for vault, we just need to do this:
```go
package client

import (
"context"

"github.com/hashicorp/vault/api"
"github.com/hashicorp/vault/api/auth/kubernetes"
)

func provideK8sAuth(ctx context.Context, client *api.Client, roleName string) error {
k8sAuth, err := kubernetes.NewKubernetesAuth(roleName)
if err != nil {
return err
}

authInfo, err := client.Auth().Login(ctx, k8sAuth)
if err != nil {
return err
}

return nil
}
```

Start by tracing the Go entry points shown in the issue: api.NewClient, ACL().Login(), and ACLLoginParams, then compare the requested flow with the Vault Kubernetes authentication example. Determine how a successful login should update or reuse the client configuration. Done means a Kubernetes service-account login authenticates the Consul client without requiring callers to construct a second client.

Written by the indexing model from the issue text.