[Operator] Support for multiple site masters

When moving the cross-site communication to Gossip Router tunnels (or skupper), add an option to configure the number of site master. 
This option is already available in the RHDG image.

For the record, Gossip Route tunneling is implemented here: https://github.com/pruivo/infinispan-operator/tree/t_xsite_tunnel

Changes required:

• It needs to use the Gossip Router shipped with RHDG image (instead of creating a new image). It required a new entrypoint
• Then, we can add the multiple site master configuration.