[Elastic Agent] Fix picking correct policy id for fleet-server (#25352)

When running the container command, the policy id configured in the fleet-setup.yml file was only picked up, when fleet-server was not enabled. If a fleet-server policy is set, this will be set as the default.

Later on this setup call should be improved that not both setups are possible. Currently it could be that the fleet enroll and fleet server setup policy are not identical.

To partially test this PR, I did run the elastic agent locally as following:

```
sudo STATE_PATH=${GOPATH}/src/github.com/elastic/beats/x-pack/elastic-agent/state ./elastic-agent container
```

Adjust the path to your needs. In addition, I put the currently checked in fleet-setup.yml file into state directory. In parallel, an elastic-stack setup was running.

x-pack/elastic-agent/CHANGELOG.next.asciidoc

@@ -55,7 +55,8 @@
 - Fixed: limit for retries to Kibana configurable {issue}25063[25063]
 - Fix issue with status and inspect inside of container {pull}25204[25204]
 - Remove FLEET_SERVER_POLICY_NAME env variable as it was not used {pull}25149[25149]
-- Reduce log level for listener cleanup to debug {pull}25274
+- Passing in policy id to container command works {pull}25352[25352]
+- Reduce log level for listener cleanup to debug {pull}25274[25274]
 
 ==== New features
 

x-pack/elastic-agent/pkg/agent/cmd/container.go

@@ -139,8 +139,8 @@ func logError(streams *cli.IOStreams, err error) {
 	fmt.Fprintf(streams.Err, "Error: %v\n", err)
 }
 
-func logInfo(streams *cli.IOStreams, msg string) {
-	fmt.Fprintln(streams.Out, msg)
+func logInfo(streams *cli.IOStreams, a ...interface{}) {
+	fmt.Fprintln(streams.Out, a...)
 }
 
 func logContainerCmd(streams *cli.IOStreams, cmd *cobra.Command) error {
@@ -292,10 +292,11 @@ func runContainerCmd(streams *cli.IOStreams, cmd *cobra.Command, cfg setupConfig
 				return err
 			}
 		}
-		policyID := ""
+		policyID := cfg.FleetServer.PolicyID
 		if policy != nil {
 			policyID = policy.ID
 		}
+		logInfo(streams, "Policy selected for enrollment: ", policyID)
 		cmdArgs, err := buildEnrollArgs(cfg, token, policyID)
 		if err != nil {
 			return err