[feature] Allow configuring the full domain for the workload service proxy

[utkuozdemir]

Currently we only allow --workload-proxying-subdomain, which makes the workload proxy services to be served at the same level as Omni, from a different domain (it is not really a subdomain). This was done this way for our SaaS, but we can add another config flag to specify the full domain to provide more flexibility to on-prem setups. (For example, real subdomains to Omni could be used, or completely another domain).

[logaritmisk]

This would be amazing! I currently have two instances of Omni running, and right now I have to do some less nice things to get that to work properly.

If it would be possible, it would be nice as well to have a toggle to remove the instance name suffix in the workload proxy url. As an example the address I get now is h2ct44-omni1.omni1.infra.my-domain.org, and it would be nice to remove that duplicate -omni1.

Also (sorry for spamming) I'm having issues to access the workloads with this setup. I can only access workloads from the instance that I most recently logged into. Even if I have logged in on both, one will always return a 403. My guess is due to the cookies publicKeyIdSignatureBase64 and publicKeyId both are on the parent domain. So in my case the domains for omni is omni1.infra.my-domain.org and omni2.infra.my-domain.org, but the cookies are on .infra.my-domain.org. So when I login on one instance they are overwritten. Could maybe this be related to how domain is handled for workload proxy? If not, I will create another ticket for that :)