feat: increase configuration options and fix bugs after the python3 upgrade

[teresalves]

Related to this issue: https://github.com/napalm-automation/napalm-logs/issues/382

Summing up, this PR fixes several problems:

• Lack of configurability for the kafka publishers, which are particularly useful for higher payloads
• Adding a backlog option for the internal zmq configurations, since the default is somewhat low
• the python3 kafka producer only accepts bytes and the zmq only accepts strings. So we had to encode the strings in the kafka publisher
• The "metrics_include_attributes" were new are really heavy, so they were set to False by default (people can still turn them on) - prometheus might not like this new inflow so we should just turn them on if needed.
• changed some logs from info to debug because they were not adding a lot of value when in info and ended up just spamming the logs

We have tested these changes on our side (although the kafka opts were hardcoded in a patch and not added thgough the configs)

The docs here were updated to contemplate these changes too.

Let me know what you think @mirceaulinic 😄