Fix kubectl --context and --cluster completions for persistent flags

Wire up the 'context' and 'cluster' generators to the persistent --context
and --cluster options on the root kubectl command. Previously these options
had no generatorName, so completions like 'kubectl get --context <Tab>'
would not suggest context names.

Also fix a typo in the CLUSTER_GENERATOR: 'config get_clusters' (underscore)
should be 'config get-clusters' (hyphen), matching the actual kubectl
subcommand.

Fixes: APP-3477
Refs: warpdotdev/warp#5186

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: oz-agent

command-signatures/json/kubectl.json

@@ -7039,15 +7039,19 @@
         {
             "name": "--cluster",
             "args": {
-                "name": "cluster"
+                "name": "cluster",
+                "generatorName": "cluster",
+                "skipGeneratorValidation": false
             },
             "description": "The name of the kubeconfig cluster to use",
             "isPersistent": true
         },
         {
             "name": "--context",
             "args": {
-                "name": "context"
+                "name": "context",
+                "generatorName": "context",
+                "skipGeneratorValidation": false
             },
             "description": "The name of the kubeconfig context to use",
             "isPersistent": true

command-signatures/src/generators/kubectl.rs

@@ -182,7 +182,7 @@ lazy_static! {
             );
     pub(super) static ref CLUSTER_GENERATOR: Generator =
             Generator::command_from_tokens(
-                |tokens, _, env_vars| kubectl_script(env_vars, tokens, CommandBuilder::single_command("config get_clusters")),
+                |tokens, _, env_vars| kubectl_script(env_vars, tokens, CommandBuilder::single_command("config get-clusters")),
                 |output| match KubetctlStatus::from_output(output) {
                     KubetctlStatus::ConnectedToCluster | KubetctlStatus::GeneralError => {
                         GeneratorResults::default()