applier: allow to specify authentication method

The authentication method can be specified via the 'auth_type' uri
parameter, e.g.

  box.cfg({replication = 'user:password@host:port?auth_type=chap-sha1'})

The only authentication method supported by Community Edition (CE)
is 'chap-sha1' so we don't document or announce this feature in CE.
More methods and tests will be added to Enterprise Edition (EE).

Part of #7988

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