[server] rewrite configuration to use a single config source

[AlexTugarev]

currently the server component's config consists of a number of env vars (which might be rendered from secrets) and mounts.

as suggested by @csweichel, it would be best to rewrite the configuration of the server component (perhaps payment as well, as they share some of the configuration,) to use a single source. advantages expected by this change are:

• make telepresence easier
• reduce turnarounds when working on changes related to payment or github

[geropl]

It turns out the helm chart and parsing interaction in Env is rather complicated. To make sure we do not miss any variance we take a 2 step approach:

1. Introduce new Config shape which contains everything from Env (minus some basic refactoring and cleanup). This is not used yet to make sure we don't break anything, but instead just printed out on startup for reference.
2. The next step is to ease the process of serializing->deserializing the config from

[geropl]

Re-opening as #4882 was only the 1st of 2 PRs.

[geropl]

While a biggest chunk has been merged, there are still some ToDos left:

• deploy to prod
• cleanup gitpod-io ([server] Remove legacy configuration #5496)
• cleanup gitpod-com (https://github.com/gitpod-com/gitpod/pull/5874)