Fix: update data_yandex_mdb_kafka_user documentation

[al-cheb]

The data resource doesn't support the password argument, only cluster_id and name arguments could be passed (https://github.com/yandex-cloud/terraform-provider-yandex/blob/master/yandex/data_source_yandex_mdb_kafka_user.go). If we set the password we will get an error like:

 Error: Value for unconfigurable attribute
│ 
│   with data.yandex_mdb_kafka_user.this,
│   on main.tf line 68, in data "yandex_mdb_kafka_user" "this":
│   68:   password = "abc"
│ 
│ Can't configure a value for "password": its value will be decided automatically based on the result of applying this configuration.

[saiks24]

Hi al-cheb! Thank you for your interest here.
Yep, it looks like the documentation for this data source is wrong. I've provided information about this issue to the developers. I'll return asap with new information.

[al-cheb]

@saiks24, hey, any updates?