listcomponents: introduce new internal tool to list components (#129)

This tool lists all registered components with their stability.

internal/cmd/listcomponents/main.go

@@ -0,0 +1,34 @@
+// Command listcomponents dumps the list of known Alloy components with their
+// stability.
+package main
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+	"text/tabwriter"
+
+	"github.com/grafana/alloy/internal/component"
+
+	_ "github.com/grafana/alloy/internal/component/all" // Import all component definitions
+)
+
+func main() {
+	components := component.AllNames()
+	sort.Strings(components)
+
+	tw := tabwriter.NewWriter(os.Stdout, 0, 8, 0, '\t', 0)
+	defer func() { _ = tw.Flush() }()
+
+	for _, name := range components {
+		reg, ok := component.Get(name)
+		if !ok {
+			// Not possible, but we'll ignore it anyway.
+			continue
+		}
+
+		stability, _ := strconv.Unquote(reg.Stability.String())
+		fmt.Fprintf(tw, "%s\t%s\n", reg.Name, stability)
+	}
+}