Polish "reduce metadata" feature

[bendrucker]

We noticed our log volume has been increasing pretty steadily as we move apps onto Kubernetes while the line count has remained unchanged. We attributed this to the additional k8s metadata in each line. While we include some bits of data in the _source* fields, we do want to keep some info around to ensure we can identify every pod from its logs. Was super pleased to discover that this was added a month ago!

I noticed that the docs needed some love and that a property was missing. Changes:

• Includes namespace_name as described in the original PR. Without a namespace, a pod cannot be uniquely identified.
• Adds full documentation around which properties are excluded/included and why
• Avoids focusing on the annotation part of the feature (mentions the global env var and emphasizes behavior over configuration).
• Fixes broken TOC link
• Updates to bundler@2 (unrelated, but required to run tests)

[frankreno]

LGTM

[frankreno]

@bendrucker - give me a week to see if we get anything else coming in or if i have time to tackle some other enhancements before i cut a new image.

[bendrucker]

Sounds good. We're not desperate for the namespace_name, just seemed worth fixing in the midst of docs tweaking.