lib-sieve: util: rfc2822: Added rfc2822_header_write_address() which allows adding a header with one or more addresses.

It applies UTF8 encoding only when the address string somehow contains 8-bit characters.
Sieve addresses are supposed to have any UTF8 characters in the phase MIME-encoded, not literal 8-bit characters.
However, this has been allowed from the beginning, so disabling the old behavior may break existing installations.
This function allows supporting both options.