Zone: force creation in lowercase

[andre8244]

The zone page shows special icons if the zone has a specific name, like 'guests'. If the zone is named in uppercase, like GUESTS the icon is not displayed. All the zones are displayed always in uppercase inside the UI.

Suggested change:

• the UI must force the zone name in lowercase when saving it to the db
• the UI must always display the zones in uppercase (this should be already true)

Private discussion: https://mattermost.nethesis.it/nethesis/pl/5nmu49u5jf8f8g97nzymgky3br

[andre8244]

Testing image: 23.05.3-ns.0.0.5-rc2-73-g6b92586

[francio87]

confirm, fixed.