Sources with multiple sub-domains are not working

[zarov]

Context

Sub-domains URL was added last year (#1189), to allow better load balancing on servers. While tests were added, we didn't test it with a real use case. You can try it with the following source:

const tmsSource = new itowns.TMSSource({
    url: 'https://${u:a|b|c|d}.data.osmbuildings.org/0.2/anonymous/tile/15/${x}/${y}.json',
    tileMatrixSet: 'PM',
    isInverted: true,
    projection: 'EPSG:4326',
    format: 'application/json',
});

Expected Behavior

This should work.

Actual Behavior

It doesn't. Instead, it stops here, and throws this error: Uncaught TypeError: Failed to construct 'URL': Invalid URL.

Possible Cause/Fix/Solution

Change the way the host is read, by adding either a queue by subdomain(a.server.geo, b.server.geo and c.server.geo for ${u:a|b|c}.server.geo), or a host minus the subdomain, as a general queue (server.geo for ${u:a|b|c}.server.geo)