config: add a .hg/hgrc-not-shared which won't be shared in share-safe mode
Previous patches add a safe mode for sharing repositories which involve sharing
of source requirements and config files.
In certain situations we might need to add a config to source repository which
we does not want to share. For this, we add a `.hg/hgrc-not-shared` which won't
be shared.
This also adds a `--non-shared` flag to `hg config` command to see the
non-shared config.
Differential Revision: https://phab.mercurial-scm.org/D8673
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true