Create Public `staging` server

[Alex4386]

Currently, Testing Full functionality of Meiling Gatekeeper requires a proper frontend:

Which is available as following:

• Stella IT's proprietary frontend (hosted on Stella IT Accounts)
• an open-source frontend based on React (https://github.com/stella-IT/meiling-dev.stella-it.com)
  -> development was ceased due to favor of new proprietary frontend based on vue + nuxt.js.

But testing requires proper frontend at the moment.
Therefore, We can host Stella IT's proprietary frontend (with removed some proprietary stuff that only works on Stella IT's internal fork. e.g. Stella IT Korean ID Verification System, E2E Session Exchange) on fe.staging.meili.ng for everyone to test it out.

[Alex4386]

staging branch created

[Stella-IT-Bot]

It seems @kdhkr is working on Proof of Concept open-source frontend for meiliNG. separating the issue.