feat(transform): Add Metrics Bytes Transform

[jshlbrd]

Description

• Adds a transform for emitting a metric that contains the amount of bytes passed through the application

Motivation and Context

It's not unusual for a data processing system to provide metrics on both the count and volume of messages processed; since a Metrics Count transform exists, this adds the complementary metric. This is useful for anyone using AWS or external services that don't readily make this information available.

How Has This Been Tested?

This can be integration tested locally:

make build-config
make build-go
./examples/cmd/client/file/substation/substation -config examples/config/transform/utility/message_bytes/config.json -file examples/config/transform/utility/message_bytes/data.jsonl

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.