`login` and `password` fields in URI table

Related dev. issue(s): https://github.com/tarantool/tarantool/issues/9435

Product: Tarantool (uri module)
Since: 3.0
Root document: https://docs.d.tarantool.io/en/doc/3.0/reference/reference_lua/uri/#uri-parse
SME: @ ImeevMA

Details

Now uri.parse() can parse a table containing the login and
password fields. Values from these fields take precedence over values
obtained from the string URI. For example, login and password of
{uri = 'one:two:localhost:3301, login = 'alpha', password = 'omega'}
will be alpha and omega respectively. If the login field is set
and the password field is not set, the password is set to nil.
If the password field is set, the login field must be present.
Requested by @ ImeevMA in https://github.com/tarantool/tarantool/commit/c03b8856b329c93e57c2b67f7a89151be960a02c.

Open the URI reference at the linked root document and review the uri.parse() table-argument documentation. Document the login and password fields, their precedence over URI-string values, and the validation rules described in the issue. Done means the 3.0 URI reference accurately explains these fields with a matching example.