Unable to ingest data from kafka in protobuf format

I'm running `apache/druid:31.0.0` in Docker locally.
```
syntax = "proto3";

package com.example.kafka.event.v1;

option java_multiple_files=true;
option java_package = "com.example.kafka.event.v1";

message Event {
int64 timestamp = 1;
optional string identity_id = 2;
optional string clientId = 3;
optional string firstName = 4;
optional string lastName = 5;
optional string email = 6;
optional string phone = 7;
optional string productId = 8;
optional int32 allItems = 9;
optional int32 usedItems = 10;
}
```
I used this command to generate the .desc `protoc -o event.desc --proto_path=proto proto/com/example/kafka/event/v1/event.proto `
And mounted it in this folder /opt/druid/proto-descriptors/
In my KafkaProducer I use the Event class and these properties
```
properties.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
properties.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,
KafkaProtobufSerializer.class);
properties.put(KafkaProtobufSerializerConfig.SCHEMA_REGISTRY_URL_CONFIG, "http://localhost:8084");
```

I can access the event.desc when I exec in the broker/historical/middlemanager
This is the config for Druid
```
"protoBytesDecoder": {
"type": "file",
"descriptor": "file:///opt/druid/proto-descriptors/event.desc",
"protoMessageType": "com.example.kafka.event.v1.Event"
}
```
But I get this error either in supervisor or just using Load data tab
```
Failed to submit supervisor: Cannot construct instance of `org.apache.druid.data.input.protobuf.FileBasedProtobufBytesDecoder`, problem: Cannot read descriptor file: file:/opt/druid/proto-descriptors/event.desc at [Source: (org.eclipse.jetty.server.HttpInputOverHTTP); line: 1, column: 341] (through reference chain: org.apache.druid.indexing.kafka.supervisor.KafkaSupervisorSpec["spec"]->org.apache.druid.indexing.kafka.supervisor.KafkaSupervisorIngestionSpec["ioConfig"]->org.apache.druid.indexing.kafka.supervisor.KafkaSupervisorIOConfig["inputFormat"]->org.apache.druid.data.input.protobuf.ProtobufInputFormat["protoBytesDecoder"])
```

I tried Schema registry as well. I did a POST to` locahlost:8084/subjects/test/vesrions` with payload
{
"schemaType": "PROTOBUF",
"schema": "syntax = \"proto3\";\n\npackage com.example.kafka.event.v1;\n\n option java_multiple_files=true;\n option java_package = \"com.example.kafka.event.v1\";\n\n message Event {\n int64 timestamp = 1;\n optional string identity_id = 2;\n optional string clientId = 3;\n optional string firstName = 4;\n optional string lastName = 5;\n optional string email = 6;\n optional string phone = 7;\n optional string productId = 8;\n optional int32 allItems = 9;\n optional int32 usedItems = 10;\n}"
}

Downloaded all suggested libraries and put them in (tried both) `/opt/druid/extensions/protobuf-extensions` and `/opt/druid/extensions/druid-protobuf-extensions` also added in environment file `DRUID_CLASSPATH=/opt/druid/extensions/druid-protobuf-extensions/*:/opt/druid/proto-descriptors/*`(I tried echo $DRUID_CLASSPATH and it had only -CLASSPATH, so that's not really working):

- common-config-6.0.1.jar
- common-utils-6.0.1.jar
- kafka-protobuf-provider-6.0.1.jar
- kafka-protobuf-serializer-6.0.1.jar
- kafka-schema-registry-client-6.0.1.jar
- kotlin-stdlib-1.4.0.jar
- wire-schema-3.2.2.jar

I did also try just the suggested ones in the repo (still not working):
- https://packages.confluent.io/maven/io/confluent/kafka-protobuf-provider/6.0.1/kafka-protobuf-provider-6.0.1.jar
- https://repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/1.4.0/kotlin-stdlib-1.4.0.jar
- https://repo1.maven.org/maven2/com/squareup/wire/wire-schema/3.2.2/wire-schema-3.2.2.jar

When I try to submit a supervisor
```
{
"type": "kafka",
"spec": {
"ioConfig": {
"type": "kafka",
"consumerProperties": {
"bootstrap.servers": "localhost:9092"
},
"topic": "events",
"inputFormat": {
"type": "protobuf",
"protoBytesDecoder": {
"type": "schema_registry",
"url": "http://localhost:8084"
}
},
"useEarliestOffset": true
},
"tuningConfig": {
"type": "kafka"
},
"dataSchema": {
"dataSource": "events-proto",
"timestampSpec": {
"column": "time",
"format": "posix"
},
"dimensionsSpec": {
"dimensions": [
"identity_id",
"clientId",
"firstName",
"lastName",
"email",
"phone",
"productId",
{
"type": "long",
"name": "allItems"
},
{
"type": "long",
"name": "usedItems"
}
]
},
"granularitySpec": {
"queryGranularity": "none",
"rollup": false,
"segmentGranularity": "day"
}
}
}
}
```
I get this:
```
Failed to submit supervisor: Cannot construct instance of `org.apache.druid.data.input.protobuf.SchemaRegistryBasedProtobufBytesDecoder`, problem: io/confluent/kafka/schemaregistry/protobuf/ProtobufSchemaProvider at [Source: (org.eclipse.jetty.server.HttpInputOverHTTP); line: 1, column: 237] (through reference chain: org.apache.druid.indexing.kafka.supervisor.KafkaSupervisorSpec["spec"]->org.apache.druid.indexing.kafka.supervisor.KafkaSupervisorIngestionSpec["ioConfig"]->org.apache.druid.indexing.kafka.supervisor.KafkaSupervisorIOConfig["inputFormat"]->org.apache.druid.data.input.protobuf.ProtobufInputFormat["protoBytesDecoder"])
```
I tried all the steps provided and even more, but I'm not getting anywhere. The data is being read from the topic, but I cannot parse it.
[https://github.com/Godin/apache-druid/blob/master/docs/development/extensions-core/protobuf.md](https://github.com/Godin/apache-druid/blob/master/docs/development/extensions-core/protobuf.md)

When I tried the `/extentions/protobuf-extentions` folder from this example, the broker/historical and middle manager just all crashed
[https://blog.hellmar-becker.de/2022/05/26/ingesting-protobuf-messages-into-apache-druid/](https://blog.hellmar-becker.de/2022/05/26/ingesting-protobuf-messages-into-apache-druid/)

Feels like something is missing from the explanations in the documentation.

Start with docs/development/extensions-core/protobuf.md and compare its protobuf decoder configuration with the Docker setup and supervisor JSON described here. Trace the file-based and schema-registry entry points mentioned in the error messages, then document the required dependencies, classpath, and descriptor mounting steps so a fresh setup can parse Kafka protobuf data without crashing.

Written by the indexing model from the issue text.