[DOP-29496] Load settings from config.yml

[dolfinus]

Change Summary

The main way to configure SyncMaster is now config.yml. It is still possible to set environment variables to override some settings, but it is less secure and cumbersome.

From source code perspective not much have changed. Most of changed are related to documentation and to logging config (which can be now configured directly via config.yml instead of passing hardcoded preset name).

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
syncmaster/server
__init__.py	40	3	92%	75–77
syncmaster/server/scripts
manage_superusers.py	68	21	69%	52–54, 72–74, 90–91, 93–95, 97–99, 101–102, 104, 108–109, 111, 113
syncmaster/server/settings/server
static_files.py	14	7	50%	33–39
syncmaster/worker
transfer.py	62	7	88%	51–52, 83–86, 101
syncmaster/worker/settings
hwm_store.py	18	3	83%	65–67
TOTAL	5036	280	94%

[dolfinus]

I can split this PR onto 2 - one with config.yml, and another one with just logging configuration.

[TiGrib]

Is it for debugging ?

[dolfinus]

Fixed in develop branch