Replace `service-password-file` variable with .picodata-cookie

Summary

Current patch introduces the following changes:

• CLI argument service_password_file that was used to setup password for pico-service has been removed
• Password for pico-service can be setup via special file .picodata-cookie which must be located inside instance directory

In our python API the password for pico-service used to be initialized manually by sending service_password_file parameter during instance creation. Instead of this, from now, if instance._service_password is initialized, the file .picodata-cookie is created inside instance_dir during instance creation.

From now, you can setup password for instance using method:

instance.set_service_password("s3cr3t")

Also you can setup password for new instance by sending it as argument through cluster:

cluster.add_instance(service_password="s3cr3t")

or setup one global password for all instances in the cluster, this service_password will be used later when you add new instances:

cluster.set_service_password(service_password="s3cr3t")

• Close #1249 (closed)

• Cherry-pick to: none

• Docs follow-up: docs#466 (closed)

• Changelog is updated

• See also #1170 (closed)

Closes #1249 (closed)