Support complex domain names

[lkingland]

https://github.com/boson-project/faas/blob/fbab8c09d05e0f08c5320c0d16b9508203e458d1/knative/deployer.go#L35-L42

When validating if the name is valid, we should consider the fact that 1) some DNS names have multiple levels. for example .co.uk and 2) the system supports multiple-level subdomains. for example cdn1.us-west-2.www.example.com. These conditions are supported by the CLI, by the name path-derivation mechanism, and by the KNative routing layer Kourier. Therefore updating this code to support these conditions should be the only change necessary to make it work throughout the system.

In both cases, these vagaries of domains can be addressed using the Go publicsuffix package.

One caviat: we should also consider that a common use case will be to flag a Function as "internal", meaning that it will could be suffixed with .cluster.local. We should also confirm that the publicsuffix package understands this "non-public" yet conformant suffix, supporting it manually if necessary.

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This issue is stale because it has been open for 90 days with no activity. It will automatically close after 30 more days of inactivity. Reopen the issue with /reopen. Mark the issue as fresh by adding the comment /remove-lifecycle stale.