feat(metrics): support to set default dimension in EphemeralMetrics

[leandrodamascena]

Issue number: #2676

Summary

Changes

This PR introduces the enhancement of the EphemeralMetrics class. You can now use the set_default_dimensions method or the default_dimensions parameter in the log_metrics decorator to persist dimensions across Lambda invocations.
If you'd like to remove them at some point, you can use clear_default_dimensions method.

User experience

Using log_metrics decorator

from aws_lambda_powertools.metrics import MetricUnit, EphemeralMetrics
from aws_lambda_powertools.utilities.typing import LambdaContext

ephemeral = EphemeralMetrics(namespace="POWERTOOLS")


@ephemeral.log_metrics(
    default_dimensions={'stage': 'prod'}
)
def lambda_handler(event: dict, context: LambdaContext):
    ephemeral.add_metric(name="OrderCount", unit=MetricUnit.Count, value=8)

Using set_default_dimensions

from aws_lambda_powertools.metrics import MetricUnit, EphemeralMetrics
from aws_lambda_powertools.utilities.typing import LambdaContext

ephemeral = EphemeralMetrics(namespace="POWERTOOLS")
ephemeral.set_default_dimensions(stage="prod")


@ephemeral.log_metrics
def lambda_handler(event: dict, context: LambdaContext):
    ephemeral.add_metric(name="OrderCount", unit=MetricUnit.Count, value=8)

Checklist

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• Meet tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Is this a breaking change?

RFC issue number:

Checklist:

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

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