Provide mechanism or guidance on how to integrate networks

[lgfa29]

Proposal

Nomad allows operators to create multiple custom CNI networks and have allocations pick and choose which ones to use. But mixing multiple networks may not work out-of-the-box without additional manual configuration from users and it may not be clear what is needed.

Use-cases

Create multiple CNI networks and have them communicate with each other.

Attempted Solutions

N/A

Note
Issue extracted from #13824. Refer to that issue for more context.