Track unsearchable plans in monthly analytics

[ajparsons]

Currently we track overall councils with a plan, but don't detail the "unsearchable" ones (html sites we haven't indexed).

There weren't many of these last time I checked, but this is important to understand in terms of basing analysis on "all plans", if there are plans we're missing from search (especially if that's because they're doing something we otherwise like for acccessbility reasons!)