Add workers to `tcp`, `udp`, and `forward` input plugins

[lecaros]

Is your feature request related to a problem? Please describe.

The in_tcp, in_udp, and in_forward plugins don't support the workers configuration that HTTP-based plugins have. This means these plugins can only use one thread to handle incoming traffic, which can become a bottleneck when processing high volumes of data.

HTTP plugins like in_http, in_splunk, and in_opentelemetry already support workers (recently added). This allows them to use multiple threads and better utilize CPU cores.

Describe the solution you'd like

Add a workers option to in_tcp, in_udp, and in_forward plugins, similar to what exists for HTTP plugins.

This would:

1. Allow users configure multiple worker threads to handle connections.
2. Better utilize multi-core CPUs when handling high traffic.
3. Keep the current behavior by default (workers=1).

Describe alternatives you've considered

• Running multiple Fluent Bit instances with different ports (or scale in k8s deployments) - adds complexity and needs external load balancing.