Add ability to set version from app.locals

[rgwozdz]

Currently, the feature-server version reported by the service and layer metadata routes is hardcoded (10.51, 10.5.1). This PR allows the version to be set dynamically by passing in configuration via the Express req.app.locals. If the Express implementation (e.g. Koop instance) sets the following:

koop.server.locals.config = {
  featureServer: {
    currentVersion: 10.81,
    fullVersion: '10.8.1'
  }
}

the service and layer metadata response will return the set values.