feat: show agent version in UI and CLI (#3709)

This commit adds the ability for agents to set their version upon start.
This is then reported in the UI and CLI.

cli/cliui/resources_internal_test.go

@@ -0,0 +1,50 @@
+package cliui
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenderAgentVersion(t *testing.T) {
+	t.Parallel()
+	testCases := []struct {
+		name          string
+		agentVersion  string
+		serverVersion string
+		expected      string
+	}{
+		{
+			name:          "OK",
+			agentVersion:  "v1.2.3",
+			serverVersion: "v1.2.3",
+			expected:      "v1.2.3",
+		},
+		{
+			name:          "Outdated",
+			agentVersion:  "v1.2.3",
+			serverVersion: "v1.2.4",
+			expected:      "v1.2.3 (outdated)",
+		},
+		{
+			name:          "AgentUnknown",
+			agentVersion:  "",
+			serverVersion: "v1.2.4",
+			expected:      "(unknown)",
+		},
+		{
+			name:          "ServerUnknown",
+			agentVersion:  "v1.2.3",
+			serverVersion: "",
+			expected:      "v1.2.3",
+		},
+	}
+	for _, testCase := range testCases {
+		testCase := testCase
+		t.Run(testCase.name, func(t *testing.T) {
+			t.Parallel()
+			actual := renderAgentVersion(testCase.agentVersion, testCase.serverVersion)
+			assert.Equal(t, testCase.expected, actual)
+		})
+	}
+}