[GLA Analytics] Add UI for Google Campaigns metrics menu

[rachelmcr]

We need to add the UI for a menu to select the metric to display on the card:

• Row with the label Metric and the selected metric on the left, and an icon to open the menu on the right.
• Menu has a list of all available metrics, with a checkmark next to the selected metric.
• Tapping a new metric reloads the card data for the newly selected metric.

Metric menu (closed)	Metric menu (open)

[dangermattic]

Thanks for reporting! 👍