fix: Add new line while inspecting file contents (#1477)

## Description:
<!-- Describe this change, how it works, and the motivation behind it.
-->
Reader did not include break char (new lines), so the writer contained
no new lines, giving the wrong output on both CLI and EM UI.

## Is this change user facing?
YES
<!-- If yes, please add the "user facing" label to the PR -->
<!-- If yes, don't forget to include docs changes where relevant -->

## References (if applicable):
<!-- Add relevant Github Issues, Discord threads, or other helpful
information. -->
Closes #1417
Closes #1042

core/server/api_container/server/api_container_service.go

@@ -904,7 +904,7 @@ func getTextRepresentation(reader io.Reader, lineCount int) (*string, error) {
 				return nil, stacktrace.NewError("File has no text representation because '%v' is not printable", char)
 			}
 		}
-		textRepresentation.WriteString(line)
+		textRepresentation.WriteString(fmt.Sprintf("%s\n", line))
 	}
 
 	if err := scanner.Err(); err != nil {

core/server/api_container/server/api_container_service_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/kurtosis-tech/kurtosis/api/golang/core/kurtosis_core_rpc_api_bindings"
 	"github.com/kurtosis-tech/kurtosis/container-engine-lib/lib/backend_interface/objects/port_spec"
 	"github.com/stretchr/testify/require"
+	"strings"
 	"testing"
 )
 
@@ -35,3 +36,17 @@ func TestOneToOneApiAndPortSpecProtoMapping(t *testing.T) {
 		seenPortSpecProtos[portSpecProto] = apiPortProto
 	}
 }
+
+func TestGetTextRepresentation(t *testing.T) {
+	input := `my
+line
+input
+`
+	expectedOutput := `my
+line
+`
+	output, err := getTextRepresentation(strings.NewReader(input), 2)
+	require.NoError(t, err)
+	require.NotNil(t, output)
+	require.Equal(t, expectedOutput, *output)
+}

internal_testsuites/golang/testsuite/upload_download_files_test/upload_download_file_test.go

@@ -23,7 +23,7 @@ const (
 	archiveDirectoryTestPattern    = "upload-test-golang-"
 	archiveSubDirectoryTestPattern = "sub-folder-"
 	archiveFileTestPattern         = "test-file-"
-	archiveTestFileContent         = "This file is for testing purposes."
+	archiveTestFileContent         = "This file is for testing purposes.\n"
 
 	numberOfTempTestFilesToCreateInSubDir     = 3
 	numberOfTempTestFilesToCreateInArchiveDir = 1