cli: do not hide the resource HCL parsing error and replace it with a JSON error (#19107)

We serially attempt to decode resources in the consul resource apply command
using HCL and then falling back on JSON. This causes the HCL errors to be 
dropped completely in the case where the HCL decode failed due to a typo 
instead of it actually being JSON instead.

This PR proposes sniffing to see if the first non-whitespace character in the 
input is { and if so treat it as JSON, otherwise as HCL and not 
double-decode on error.

command/resource/helper.go

@@ -8,10 +8,13 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"google.golang.org/protobuf/encoding/protojson"
-	"google.golang.org/protobuf/types/known/anypb"
 	"net/http"
 	"strings"
+	"unicode"
+	"unicode/utf8"
+
+	"google.golang.org/protobuf/encoding/protojson"
+	"google.golang.org/protobuf/types/known/anypb"
 
 	"github.com/hashicorp/consul/agent/consul"
 	"github.com/hashicorp/consul/command/helpers"
@@ -34,11 +37,13 @@ type Tenancy struct {
 	Partition string `json:"partition"`
 	PeerName  string `json:"peerName"`
 }
+
 type Type struct {
 	Group        string `json:"group"`
 	GroupVersion string `json:"groupVersion"`
 	Kind         string `json:"kind"`
 }
+
 type ID struct {
 	Name    string  `json:"name"`
 	Tenancy Tenancy `json:"tenancy"`
@@ -95,17 +100,41 @@ func ParseResourceFromFile(filePath string) (*pbresource.Resource, error) {
 		return nil, fmt.Errorf("Failed to load data: %v", err)
 	}
 	var parsedResource *pbresource.Resource
-	parsedResource, err = resourcehcl.Unmarshal([]byte(data), consul.NewTypeRegistry())
-	if err != nil {
+	if isHCL([]byte(data)) {
+		parsedResource, err = resourcehcl.Unmarshal([]byte(data), consul.NewTypeRegistry())
+	} else {
 		parsedResource, err = parseJson(data)
-		if err != nil {
-			return nil, fmt.Errorf("Failed to decode resource from input file: %v", err)
-		}
+	}
+	if err != nil {
+		return nil, fmt.Errorf("Failed to decode resource from input file: %v", err)
 	}
 
 	return parsedResource, nil
 }
 
+// this is an inlined variant of hcl.lexMode()
+func isHCL(v []byte) bool {
+	var (
+		r      rune
+		w      int
+		offset int
+	)
+
+	for {
+		r, w = utf8.DecodeRune(v[offset:])
+		offset += w
+		if unicode.IsSpace(r) {
+			continue
+		}
+		if r == '{' {
+			return false
+		}
+		break
+	}
+
+	return true
+}
+
 func ParseInputParams(inputArgs []string, flags *flag.FlagSet) error {
 	if err := flags.Parse(inputArgs); err != nil {
 		if !errors.Is(err, flag.ErrHelp) {