fix: retry using docker-credential helpers with trailing slash on the registry URL (#2728)

Currently using the docker-credential helpers might be broken to a
missing slash on the registry address.
Some registries might have a suffixed `/` or not. To be able to deal
with both cases. We just try both approaches.

`echo "https://index.docker.io/v1" |
/usr/local/bin/docker-credential-osxkeychain get`

vs 

`echo "https://index.docker.io/v1/" |
/usr/local/bin/docker-credential-osxkeychain get `


I've tested this manually with the existing OSX test
`TestGetAuthConfigForRepoOSX` (which is skipped by default).

```
go test -run TestGetAuthConfigForRepoOSX ./container-engine-lib/lib/backend_impls/docker/docker_manager/... -v

=== RUN   TestGetAuthConfigForRepoOSX
--- PASS: TestGetAuthConfigForRepoOSX (0.06s)
```

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Author: skylenet

container-engine-lib/lib/backend_impls/docker/docker_manager/docker_auth.go

@@ -106,6 +106,26 @@ func getCredentialsFromStore(credHelper string, registryURL string) (*registry.A
 	// Prepare the helper command (docker-credential-<store>)
 	credHelperCmd := "docker-credential-" + credHelper
 
+	// First try with the original URL
+	auth, err := tryGetCredentialsWithURL(credHelperCmd, registryURL)
+	if err == nil {
+		return auth, nil
+	}
+
+	// If the URL doesn't end with a slash, try again with a trailing slash
+	if !strings.HasSuffix(registryURL, "/") {
+		auth, retryErr := tryGetCredentialsWithURL(credHelperCmd, registryURL+"/")
+		if retryErr == nil {
+			return auth, nil
+		}
+	}
+
+	// If both attempts failed, return the original error
+	return nil, err
+}
+
+// tryGetCredentialsWithURL attempts to get credentials for a specific URL
+func tryGetCredentialsWithURL(credHelperCmd string, registryURL string) (*registry.AuthConfig, error) {
 	// Execute the credential helper to get credentials for the registry
 	cmd := exec.Command(credHelperCmd, "get")
 	cmd.Stdin = strings.NewReader(registryURL)