out_kafka: increase max kafka dynamic topic length to 249 characters

[mickymiek]

This commit increases the max length of kafka dynamic topics.

As the limit previously set (64) seemed arbitrary, and kafka allows for a maximum of 249 characters per topic, I think fluentbit should reflect that limit.

Fixes #4337

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[cosmo0920]

From the Kafka documentation, this modification should be vaild:

Each sharded partition log is placed into its own folder under the Kafka log directory. The name of such folders consists of the topic name, appended by a dash (-) and the partition id. Since a typical folder name can not be over 255 characters long, there will be a limitation on the length of topic names. We assume the number of partitions will not ever be above 100,000. Therefore, topic names cannot be longer than 249 characters. This leaves just enough room in the folder name for a dash and a potentially 5 digit long partition id.
ref: https://kafka.apache.org/documentation/

[edsiper]

thank you