Issue #, if available:

Description of changes:

For minor changes such as remapping keys, removing certain keys, etc., you will no longer have to implement a whole custom formatter from BasePowertoolsFormatter.

This PR introduces a public method serialize that is called after log record processing takes place, so customers don't have to reimplement extra keys, UTC support, X-Ray (if used), etc:

UX

from aws_lambda_powertools import Logger
from aws_lambda_powertools.logging.formatter import LambdaPowertoolsFormatter

from typing import Dict

class CustomFormatter(LambdaPowertoolsFormatter):
    def serialize(self, log: Dict) -> str:
        log["event"] = log.pop("message")
        return self.json_serializer(log)

logger = Logger(service="example", logger_formatter=CustomFormatter())
logger.info("hello")

This PR also documents the use of LambdaPowertoolsFormatter as a standalone formatter:

from aws_lambda_powertools import Logger
from aws_lambda_powertools.logging.formatter import LambdaPowertoolsFormatter

formatter = LambdaPowertoolsFormatter(utc=True, log_record_order=["message"])
logger = Logger(service="example", logger_formatter=formatter)

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

Breaking change checklist

RFC issue #:

• Migration process documented
• Implement warnings (if it can live side by side)

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