[ENSCORESW-3122] Relicense Zircon from GPL to Apache-2.0

Created by: mkszuba

Zircon is distributed under the GPL yet is linked to by software packages licensed as Apache-2.0, which is not a legal combination (see e.g. https://www.apache.org/licenses/GPL-compatibility.html). This is not a problem for internal use of this software within HAVANA because the contract between Genome Research Ltd and EMBL-EBI takes precedence over generic licences, on the other hand it makes the situation complicated for potential external users. Therefore, change the licence of Zircon to Apache-2.0 (personally I would have preferred LGPL but let us be consistent with other Ensembl software products).