Add a new DLV that tracks which blocks are being used on a page

Summary

A useful metric to measure for users that interact with a page is the list of blocks included in that page.

Requirements

• Add a new dataLayer variable in the header array.
• That variable should have a comma separated list of the active blocks.
• The list should contain only blocks from planet4-blocks and gravityforms namespaces.
• Example:

  'p4_blocks' : 'articles, columns, gravityforms'

Resources

• Relevant discussion