vlagent/kafka: add optional Kafka input support to vlagent

[func25]

Is your feature request related to a problem? Please describe

It would be very useful if vlagent could optionally consume logs directly from Kafka topics in addition to the existing HTTP/Kubernetes inputs. Many users already route application logs into Kafka and would like a simple, native "Kafka (→ vlagent) → VictoriaLogs" path.

Describe the solution you'd like

The high-level idea is to add a new Kafka collector module inside vlagent

Describe alternatives you've considered

No response

Additional information

Related #12

[Sleuth56]

It would be great if Otel formatted logs could be apart of this.

[kurayama]

We had issues on our otel agent/gateway/vlagent setup due to the behavior between the kafka receiver with message marking and batch processor which effectively breaks message marking given its async nature, that leads to possible loss of logs.
It would be great to be able to get rid of the gateway and consume kafka + otel protocol directly with vlagent.