module-transaction: Add support for initiating PAM Conversations

Modules have the ability to start PAM conversations, so while the
transaction code can handle them we did not have a way to init them.
Yet.

So add some APIs allowing this, making it easier from the go side to
handle the conversations.

In this commit we only support text-based conversations, but code is
designed with the idea of supporting binary cases too.

Added the integration tests using the module that is now able to both
start conversation and handle them using Go only.

cmd/pam-moduler/tests/internal/utils/test-utils.go

@@ -118,6 +118,10 @@ func (e *SerializableError) Error() string {
 type Credentials struct {
 	User              string
 	Password          string
+	EchoOn            string
+	EchoOff           string
+	TextInfo          string
+	ErrorMsg          string
 	ExpectedMessage   string
 	CheckEmptyMessage bool
 	ExpectedStyle     pam.Style
@@ -145,9 +149,19 @@ func (c Credentials) RespondPAM(s pam.Style, msg string) (string, error) {
 
 	switch s {
 	case pam.PromptEchoOn:
-		return c.User, nil
+		if c.User != "" {
+			return c.User, nil
+		}
+		return c.EchoOn, nil
 	case pam.PromptEchoOff:
-		return c.Password, nil
+		if c.Password != "" {
+			return c.Password, nil
+		}
+		return c.EchoOff, nil
+	case pam.TextInfo:
+		return c.TextInfo, nil
+	case pam.ErrorMsg:
+		return c.ErrorMsg, nil
 	}
 
 	return "", errors.Join(pam.ErrConv,