fix: panic after revoke login

Summary

• fix: skip on_auth checks for pico service user
• fix: panic after login privilege revoked
• test: submit sql after revoke login
• test: create user with sql in test_cli_connect

Now removing/adding picodata login privilege only removes/adds tarantool usage. And the functionality of taranool session is implemented by our custom check in on_auth trigger.

After rebase on top of mr introducing pico service user, some fixes related to this user were also added.

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• Close #515 (closed)
• Close #513 (closed)
• Target branch: master
• Docs follow-up: not necessary