Audit user traffic to obsolete or unsupported views

[mattmathis]

Create a metadata tag to identify production tables and views.
Create an easily parsed log of user traffic to assets not bearing suitable tags.

Plan A: use some existing tag in the view metadata
Plan B: Add "Support-status: full" (etc) to the end of BQ table descriptions

[pboothe]

Read access logs and their controls are harder to find than write access logs