encode_cloudwatch_emf_payload: Support EMF adopted payload encoder

[cosmo0920]

To handle EMF formatting for cmetrics context, we need to add emf payload encoder for cloudwatch_logs.

[edsiper]

@cosmo0920 thanks for this.

I would suggest to rename the prototype of the API and remove the payload from the function names, e.g:

from cmt_encode_cloudwatch_emf_payload_create() to cmt_encode_cloudwatch_emf_create()

[cosmo0920]

Thanks for your suggestion. I removed 'payload' from functions and files names.

[cosmo0920]

🎉