processor_attributes: add support to handle Logs metadata (WIP)

[edsiper]

The following PR implements support to modify Logs metadata as logs attributes. The previous implementation only support traces, this patch extends it functionality.

note: this is still work in process and as of now there is only logic split with CFL and inside the processor_attributes plugin.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.