config: add `--shared` flag to edit config file of shared source With `format.exp-share-safe` enabled, we now read the `.hg/hgrc` of the shared source also. This patch adds `--shared` flag to `hg config` command which can be used to edit that shared source config file. It only works if the repository is shared one and is shared using the safe method. Differential Revision: https://phab.mercurial-scm.org/D8659