fix: wrong pico_service password + picodata expel --user

Summary

• fix: used to not provide pico_service password on initial replication configuration
• test: now conftest.Cluster.deploy sets the non-empty pico_service password for the cluster
• fix: picodata expel now accepts --user, --password-file & --auth-method parameters and behaves the same way picodata connect does with respect to credentials

Note that using picodata expel requires providing a user which is authorized to execute stored procedure .proc_expel_redirect. Currently by default the only such user is pico_service and the only way to create another user with such privileges is to go through lua.

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• Close #...
• Target branch: master
• Changes should be cherry-picked to 24.1: yes / no
• Docs follow-up: docs#199 (closed)