feat(transform): Add Metric Freshness Transform

[jshlbrd]

Description

• Adds a utility_metric_freshness transform with an example

Motivation and Context

This makes it possible to measure message / data freshness (commonly used to measure data processing systems). Unlike other metric transforms, this emits two metrics with unique attributes to differentiate them in the downstream monitoring platform. A freshness SLO can be calculated by turning these metrics into a percentage (e.g., SLO = success / (success + failure) for a particular pipeline).

It's up to the user to determine when to begin measuring freshness (as determined by the object.source_key timestamp value), but two examples are:

• Measure freshness of an individual pipeline component (using the time_now transform)
• Measure end-to-end freshness of an entire pipeline (using the timestamp value from the data source)

How Has This Been Tested?

Integration tested using the example config. End-to-end testing will come after this is merged to main (as part of testing the next release).

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.

[shellcromancer]

Code changes themselves for the feature look good. I left 2 comments on the documentation comments and usability that are non-blocking but would be good to discuss.