Add tarantool password recommendations

[LeonidVas]

According to the description here, I think it would be nice to add a recommendation to use a >= 16 length password using [a-Z0-9] and special symbols like [!$&'(|)*+,;=-_~.%].

Useful links:
https://jira.vk.team/browse/TNT-848

[p7nov]

https://www.tarantool.io/en/doc/latest/book/admin/access_control/#passwords

[andreyaksenov]

The example from the Password policy section uses all the recommendations:

https://www.tarantool.io/en/doc/latest/concepts/configuration/configuration_authentication/#password-policy