Fix validating the URL of user home sites

Home site validation used the URL regexp, but didn't anchor it. Because
of this it was possible to add text before or after the URL and have it
considered valid. For instance, this was considered a valid homesite
value: "lorem ipsum https://example.org/#foo#bar dolor sit amet"

It is possible to fix it by anchoring the regexp, but IMO it is wiser to
use the same URL validator used at other places in the site. Hence this
commit replaces this validation with the `http_url` validator used for
news links and bookmarks.

https://linuxfr.org/suivi/impossible-de-mettre-un-lien-vers-un-salon-matrix-dans-les-liens-d-une-depeche#comment-1911550

app/models/user.rb

@@ -29,8 +29,8 @@ class User < ActiveRecord::Base
   has_many :taggings, -> { includes(:tag) }, dependent: :destroy
   has_many :tags, -> { distinct }, through: :taggings
 
-  validates_format_of :homesite, message: "L’adresse du site Web personnel n’est pas valide", with: URI::regexp(%w(http https)), allow_blank: true
-  validates :homesite, length: { maximum: 100, message: "L’adresse du site Web personnel est trop longue" }
+  validates :homesite, http_url: { protocols: ["http", "https"], message: "L’adresse du site Web personnel n’est pas valide" },
+                       length: { maximum: 100, message: "L’adresse du site Web personnel est trop longue" }
   validates :name, length: { maximum: 40, message: "Le nom affiché est trop long" }
   validates :jabber_id, length: { maximum: 32, message: "L’adresse XMPP est trop longue" }
   validates :signature, length: { maximum: 255, message: "La signature est trop longue" }