Rename "xmpp" user service back to "ejabberd"

If we ever add support for others, we can combine them as "xmpp" in
helper methods

spec/models/user_spec.rb

@@ -78,9 +78,9 @@ RSpec.describe User, type: :model do
     it "returns the entries from the LDAP service attribute" do
       expect(user).to receive(:ldap_entry).and_return({
         uid: user.cn, ou: user.ou, mail: user.email, admin: nil,
-        services_enabled: ["discourse", "email", "gitea", "wiki", "xmpp"]
+        services_enabled: ["discourse", "ejabberd", "email", "gitea", "wiki"]
       })
-      expect(user.services_enabled).to eq(["discourse", "email", "gitea", "wiki", "xmpp"])
+      expect(user.services_enabled).to eq(["discourse", "ejabberd", "email", "gitea", "wiki"])
     end
   end
 
@@ -88,7 +88,7 @@ RSpec.describe User, type: :model do
     before do
       allow(user).to receive(:ldap_entry).and_return({
         uid: user.cn, ou: user.ou, mail: user.email, admin: nil,
-        services_enabled: ["gitea", "xmpp"]
+        services_enabled: ["ejabberd", "gitea"]
       })
     end
 
@@ -121,9 +121,9 @@ RSpec.describe User, type: :model do
 
     it "adds multiple service to the LDAP entry" do
       expect_any_instance_of(LdapService).to receive(:replace_attribute)
-        .with(dn, :serviceEnabled, ["discourse", "gitea", "wiki", "xmpp"]).and_return(true)
+        .with(dn, :serviceEnabled, ["discourse", "ejabberd", "gitea", "wiki"]).and_return(true)
 
-      user.enable_service([:wiki, :xmpp])
+      user.enable_service([:ejabberd, :wiki])
     end
   end
 
@@ -131,7 +131,7 @@ RSpec.describe User, type: :model do
     before do
       allow(user).to receive(:ldap_entry).and_return({
         uid: user.cn, ou: user.ou, mail: user.email, admin: nil,
-        services_enabled: ["discourse", "gitea", "xmpp"]
+        services_enabled: ["discourse", "ejabberd", "gitea"]
       })
       allow(user).to receive(:dn).and_return(dn)
     end
@@ -140,14 +140,14 @@ RSpec.describe User, type: :model do
       expect_any_instance_of(LdapService).to receive(:replace_attribute)
         .with(dn, :serviceEnabled, ["discourse", "gitea"]).and_return(true)
 
-      user.disable_service(:xmpp)
+      user.disable_service(:ejabberd)
     end
 
     it "removes multiple services from the LDAP entry" do
       expect_any_instance_of(LdapService).to receive(:replace_attribute)
         .with(dn, :serviceEnabled, ["discourse"]).and_return(true)
 
-      user.disable_service([:xmpp, "gitea"])
+      user.disable_service([:ejabberd, "gitea"])
     end
   end