Fixed unmarshalling json input into `interface{}` type (#1832)

## Changes
Fixed unmarshalling json input into `interface{}` type

Commands like `api post` support free form request input, so it should
be unmarshaled correctly

## Tests
Added regression test + E2E test pass

libs/flags/json_flag.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"reflect"
 
 	"github.com/databricks/cli/libs/diag"
 	"github.com/databricks/cli/libs/dyn/convert"
@@ -63,12 +64,25 @@ func (j *JsonFlag) Unmarshal(v any) diag.Diagnostics {
 		return diags.Extend(diag.FromErr(err))
 	}
 
+	kind := reflect.ValueOf(v).Kind()
+	if kind == reflect.Ptr {
+		kind = reflect.ValueOf(v).Elem().Kind()
+	}
+
+	if kind == reflect.Struct {
 		// Finally unmarshal the normalized data to the output.
 		// It will fill in the ForceSendFields field if the struct contains it.
 		err = marshal.Unmarshal(data, v)
 		if err != nil {
 			return diags.Extend(diag.FromErr(err))
 		}
+	} else {
+		// If the output is not a struct, just unmarshal the data to the output.
+		err = json.Unmarshal(data, v)
+		if err != nil {
+			return diags.Extend(diag.FromErr(err))
+		}
+	}
 
 	return diags
 }

libs/flags/json_flag_test.go

@@ -13,10 +13,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-type requestType struct {
-	Foo string `json:"foo"`
-}
-
 func TestJsonFlagEmpty(t *testing.T) {
 	var body JsonFlag
 
@@ -35,13 +31,13 @@ func TestJsonFlagInline(t *testing.T) {
 	err := body.Set(`{"foo": "bar"}`)
 	assert.NoError(t, err)
 
-	var request requestType
+	var request any
 	diags := body.Unmarshal(&request)
 	assert.NoError(t, diags.Error())
 	assert.Empty(t, diags)
 
 	assert.Equal(t, "JSON (14 bytes)", body.String())
-	assert.Equal(t, requestType{"bar"}, request)
+	assert.Equal(t, map[string]any{"foo": "bar"}, request)
 }
 
 func TestJsonFlagError(t *testing.T) {
@@ -50,7 +46,7 @@ func TestJsonFlagError(t *testing.T) {
 	err := body.Set(`{"foo":`)
 	assert.NoError(t, err)
 
-	var request requestType
+	var request any
 	diags := body.Unmarshal(&request)
 	assert.EqualError(t, diags.Error(), "error decoding JSON at (inline):1:8: unexpected end of JSON input")
 	assert.Equal(t, "JSON (7 bytes)", body.String())
@@ -58,7 +54,7 @@ func TestJsonFlagError(t *testing.T) {
 
 func TestJsonFlagFile(t *testing.T) {
 	var body JsonFlag
-	var request requestType
+	var request any
 
 	var fpath string
 	var payload = []byte(`{"foo": "bar"}`)
@@ -78,7 +74,7 @@ func TestJsonFlagFile(t *testing.T) {
 	assert.NoError(t, diags.Error())
 	assert.Empty(t, diags)
 
-	assert.Equal(t, requestType{"bar"}, request)
+	assert.Equal(t, map[string]any{"foo": "bar"}, request)
 }
 
 const jsonData = `