Add Missing Documentation Detector

[ScottSuarez]

Background

Users can add resources or fields. These fields may not be documented (if not auto-gen)

What kind of contribution is this issue about?

hand-written//tpgtools

Details

The stupid path is pretty simple.
(field added or resource ect)
No doc changes.
Sad face

GoogleCloudPlatform/magic-modules#6921

[iyabchen]

Some ideas/improvements:

• create a scanner to find all existing fields that are missing docs
• the detector reports all fields that are missing doc on the involved resource in the change, not limited to only new fields in the involved resource.

[melinath]

• Scanner could be good but that should be a separate ticket.
• The detector should only report missing docs for fields changed in the PR - PR authors are not responsible for changes to other fields.