Add computed to password* fields in connection resource

[sergiught]

Description

While investigating #108 using the reproducible:

resource "auth0_connection" "sample_connection" {
    name     = "sample-connection-issue108"
    strategy = "auth0"
    options {
        enabled_database_customization = "true"
        brute_force_protection         = true
        import_mode                    = false
        disable_signup                 = true
        requires_username              = false
        custom_scripts                 = {
            get_user = <<EOF
function getByEmail (email, callback) {
  return callback(new Error("Whoops!"))
}
EOF
        }
    }
}

On subsequent terraform plan's we would constantly get diffs on the password fields as the API assigns certain default values to them. This PR fixes that.

Checklist

Note: Checklist required to be completed before a PR is considered to be reviewable.

Auth0 Code of Conduct

• I have read and agreed to the terms within the Auth0 Code of Conduct

Auth0 General Contribution Guidelines

• I have read the Auth0 General Contribution Guidelines

Changes include test coverage?

• Yes
• Not needed

Does the description provide the correct amount of context?

• Yes, the description provides enough context for the reviewer to understand what these changes accomplish

Have you updated the documentation?

• Yes, I've updated the appropriate docs
• Not needed

Is this code ready for production?

• Yes, all code changes are intentional and no debugging calls are left over