Deprecate gitlab-shell.yml
Currently we have two config files in gitaly (not counting praefect). One is the main gitaly application config.toml. The other is gitlab-shell's gitlab-shell.yml. This is because the hooks that were part of gitlab-shell got moved to gitaly, and the ruby code for hooks continued to read config values from the config.yml.
This is not ideal and we need to deprecate gitlab-shell.yml by moving its config values into gitaly's application config.toml. Then gitaly can pass down these values to the ruby code via environment variables, so we only have one place where configs live in gitaly.
this includes:
- custom_hooks_dir
- gitlab_url
- http_settings
- secret_file
this will be a breaking change for 13.0. Omnibus will not be affected, but users who install from source will need to be notified via the docs that the gitlab-shell.yml is no longer supported and the configs need to move into config.toml