Support setting federation upstream uri to a list of uri

[ChunyiLyu]

Is your feature request related to a problem? Please describe.

You can set federation upstreams uri to a list of uris: https://www.rabbitmq.com/federation-reference.html#upstreams.

rabbit-hole currently has a limitation of only supporting setting federation upstream uri to a single string (related issue: michaelklishin/rabbit-hole#192). After the rabbit hole issue is resolved and released, topology operator should support multiple uris for federation upstream as well.

Describe the solution you'd like

We currently take a string value from the federation uri secret that's provided. The solution should be similar with what we are doing for schema replication endpoints, where we take in a string that's separated by a character (like ,). There will be no change in the CRD API with this solution.

[ChunyiLyu]

New rabbit-hole release contains fix: michaelklishin/rabbit-hole#193

Working on this issue now.