Fields for additional users should have defaults

[jyoungs]

TL;DR

https://github.com/terraform-google-modules/terraform-google-sql-db/blob/v21.0.0/modules/postgresql/variables.tf#L335C5-L335C13

Password is intended to be optional with the conditional (already setup) validating that password is required IFF random_password == false

IMO random_password should default to true, but that's more of an opinion.

Terraform Resources

No response

Detailed design

type = list(object({
    name            = string
    password        = optional(string, "")
    random_password = optional(bool, true)
  }))

### Additional information

_No response_