managesieve vacation: UI should allow display names in from field

[c0deright]

Current code prevents users from creating a vacation rule where the From field contains a display-name like

My Name <foo@example.com>

so the out-of-office reply would contain the header

From: My Name <foo@example.com>

Right now you're forced by UI to use

foo@example.com

which results in header

From: foo@example.com

which then results in mails likely getting marked as Junk by the receiving MTA.

It's basically the same issue as outlined in cyrusimap/cyrus-imapd#2189.

It's perfectly legal to use

vacation :days 14 :addresses ["..."] :subject "..." :from "My Name <foo@example.com>"

in a sieve script.

In fact, I just edited the sieve script with vim and did test the out-of-office reply and can confirm that the ooo email now has a header From: My Name <foo@example.com> instead of From: foo@example.com.

[alecpl]

Confirmed with RFC 5230.

[alecpl]

PR created in #6763.

[alecpl]

Done.