Resolve "Enable ActiveContext"

What does this MR do and why?

This enables the ActiveContext framework/layer and adds documentation about the activecontext.log.

Note: this is the first step of a 2-step process for enabling an ActiveContext pipeline in an instance. The second step will be addressed in #554923 (closed) (staging) and #554924 (closed) (production).

References

Issue: Enable ActiveContext (#554921 - closed)

Screenshots or screen recordings

N/A

How to set up and validate locally

N/A

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #554921 (closed)