Config file to expose all environment variables declaratively

Enhancement Type

A completely new feature

Describe the enhancement

The number of configuration options and environment variables is now quite large and unwieldy.
For more intricate setups, it'd be valuable to consolidate the dozens of environment variables down into a config file.

• I imagine the environment variables would remain for backwards compatibility and potentially be deprecated until the next major version.
• All logic that depends on environment variables could transition to reading the config file.
• The logic behind the config file could contain inline documentation that could be extracted by CI into user-facing documentation (#1440)
• A helper function would bridge the gap between new and legacy, containing a mapping of environment variables to YAML paths.
  • The helper could generate/update the new config if legacy environment variables are exposed.
  • The helper could possibly inform the user the config file has been generated/updated.
  • The log could also detail which legacy environment variables were converted.
  • The log could also state the legacy variables can be removed from the user's container spec if they wish.

The issue names no specific files, tests, or entry points; begin by mapping the existing environment-variable handling and the proposed YAML paths. Done would require a declarative config, compatibility for legacy variables, a conversion helper with logging, and coordination with documentation extraction in #1440.