software/theia: Make theiaN frontend names unique

This concerns a case of resiliency in Theia: when a resilient Theia
requests multiple import clones (by default only one is requested),
e.g. when theia0 (export) has two import clones theia1 and theia2.

Each clone requests a frontend for their theia service, which allows
the Theia editor of the clone to be accessed without doing a takeover.

Before this, all the import clones would request a frontend with the
same name. This meant that only one frontend was allocated and might
randomly redirect to one of the backup clones.

See merge request nexedi/slapos!1481