Implement new stackit_image resource and datasource (#609)

* feat: Implement image resource and datasource

* feat: Add remaining config options

* feat: Make protected field only computed

* feat: Update dependency to use IaaS beta API

* fix: Minor fix in acc test

---------

Co-authored-by: Vicente Pinto <vicente.pinto@freiheit.com>

stackit/internal/validate/testdata/file.txt

@@ -0,0 +1 @@
+I am a test file

stackit/internal/validate/validate.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"os"
 	"regexp"
 	"strings"
 	"time"
@@ -272,3 +273,21 @@ func Rrule() *Validator {
 		},
 	}
 }
+
+func FileExists() *Validator {
+	description := "file must exist"
+
+	return &Validator{
+		description: description,
+		validate: func(_ context.Context, req validator.StringRequest, resp *validator.StringResponse) {
+			_, err := os.Stat(req.ConfigValue.ValueString())
+			if err != nil {
+				resp.Diagnostics.Append(validatordiag.InvalidAttributeValueDiagnostic(
+					req.Path,
+					description,
+					req.ConfigValue.ValueString(),
+				))
+			}
+		},
+	}
+}

stackit/internal/validate/validate_test.go

@@ -682,3 +682,42 @@ func TestRrule(t *testing.T) {
 		})
 	}
 }
+
+func TestFileExists(t *testing.T) {
+	tests := []struct {
+		description string
+		input       string
+		isValid     bool
+	}{
+		{
+			"ok",
+			"testdata/file.txt",
+			true,
+		},
+		{
+			"not ok",
+			"testdata/non-existing-file.txt",
+			false,
+		},
+		{
+			"empty",
+			"",
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.description, func(t *testing.T) {
+			r := validator.StringResponse{}
+			FileExists().ValidateString(context.Background(), validator.StringRequest{
+				ConfigValue: types.StringValue(tt.input),
+			}, &r)
+
+			if !tt.isValid && !r.Diagnostics.HasError() {
+				t.Fatalf("Should have failed")
+			}
+			if tt.isValid && r.Diagnostics.HasError() {
+				t.Fatalf("Should not have failed: %v", r.Diagnostics.Errors())
+			}
+		})
+	}
+}