Handle container connection conflicts in backup strategy

- Catch ConflictException when connecting to Docker container
- Wrap exception in BackupException with detailed message

Author: nomad4tech

src/main/java/tech/nomad4/backupmanager/isolate/backup/strategy/PostgresBackupStrategy.java

@@ -105,6 +105,9 @@ public void onNext(Frame frame) {
 
         } catch (BackupException e) {
             throw e;
+        } catch (com.github.dockerjava.api.exception.ConflictException e) {
+            throw new BackupException(
+                    "Failed to connect container: " + command.getContainerId(), e);
         } catch (IOException e) {
             throw new BackupException("Failed to open output file: " + outputPath, e);
         } catch (InterruptedException e) {