Change meter.resource_metadata column type

The existing schema limits for meter.resource_metadata column to
5000 characters, which may not be enough for a large metadata
payload encoded as JSON.
Using a Text column will let us store an arbitrary amount of data
in that column without worrying about overflowing.

Closes-Bug: #1204638

Change-Id: I5eb1cdbb3d4770a8348682634a78ccb0f843c141
Merge "Change meter.resource_metadata column type"