Move 'location' from firebase.json to dataconnect.yaml

[joehan]

Description

Previously, location was provided as part of firebase.json:

## firebase.json
dataconnect: {
  source: 'dataconnect',
  location: 'us-east4',
}

Now, it is provided via dataconnect.yaml

specVersion: "v1alpha"
serviceId: "other-other-dataconnect"
location: "us-east4"

Scenarios Tested

Tested the following cases using an emulator built from HEAD:

• Deployed dataconnect, and confirmed that it uses the right location
• firebase init dataconnect writes location to dataconnect.yaml, not firebase.json
• Ran SDK generation (via dataconnect:sdk:generate and via emulator:start), and confirmed that the correct location is passed through to the generated SDKs by searching the generated code.

I also tested the cases where someone still has the old way of setting location - we show a warning if location is set in firebase.json, and error out if it is missing in dataconnect.yaml: