Fix users variable to make type property optional as per documentation

[imprateeksh]

The official documentation specifies that the user type property within the users variable should be optional.

Our current module configuration enforces the type property as a required field for each user object. This should be addressed to align with the documentation.

Currently, the users variable is defined as follows, making the type property required:

variable "users" {
  type = list(object({
    name     = string
    password = string # pragma: allowlist secret
    type     = string # "type" is required to generate the connection string for the outputs.
    role     = optional(string)
  }))
}