Implement nRF Cloud API response validation

[coderbyheart]

These API calls could use validation:

• backend/lambda/resolveSingleCellGeoLocation.ts

  Line 156 in f17d6af

  // FIXME: validate response

• backend/lambda/resolveSingleCellGeoLocation.ts

  Line 57 in f17d6af

  // FIXME: validate response

• backend/nrfcloud/createAccountDevice.ts

  Line 15 in f17d6af

  const accountDevice = await // FIXME: validate response

• backend/nrfcloud/devices.ts

  Line 185 in f17d6af

  // FIXME: validate response

• backend/nrfcloud/getDeviceShadowFromnRFCloud.ts

  Line 32 in f17d6af

  // FIXME: validate response