Reorder firebase init dataconnect prompts for better local onboarding flow.

[rosalyntan]

Description

• If there are existing services / instances, use those for setting up local files
  • Until b/368609569 is fixed, this is only for projects with billing. After, should work regardless of billing state
• If there are no existing services / instances:
  • If no billing:
    • Set up local files with defaults
  • If yes billing:
    • Ask if they want to configure backend resource, otherwise set up local files with defaults

Scenarios Tested

• project with no billing
• project with billing with existing services
• project with billing with no services, (y) for configuring backend resources
• project with billing with no services, (n) for configuring backend resources

Sample Commands

project with billing with existing services:

project with billing with no services, (n) for configuring backend resources:

[joehan]

Small type nits but lgtm otherwise

[joehan]

Nit:

Suggested change

	const choices: { name: string; value: any }[] = existingServicesAndSchemas.map((s) => {
	const choices: { name: string; value: { schema: Schema, service: Service } | undefined }[] = existingServicesAndSchemas.map((s) => {

[joehan]

If you set it above, you can remove this type declaration here because promptOnce will return a defined type.