Metric adm::get_tiles calls

[pjenvey]

Visibility into how frequently we're querying for tiles from ADM would be useful, let's add a simple counter metric for this.

┆Issue is synchronized with this Jira Task

[jrconlin]

There is a metric call on handlers/get_tiles(), which should suffice. Do you want one that is explicitly for adm?

[pjenvey]

There is a metric call on handlers/get_tiles(), which should suffice. Do you want one that is explicitly for adm?

Yea, since they're isn't a 1:1 mapping of handler::get_tiles calls to the call to adm (adm::get_tiles)