config: add --source option to include source of value Showing the source of each config option is quite useful and not something the user should have to reach for the `--debug` flag for. I updates documentation and tests, except for one place in `test-hgrc.t` where I thought the test might have been intended to also test that `--debug` results in `ui.quiet` etc being test. Differential Revision: https://phab.mercurial-scm.org/D10668

--- a/relnotes/next	Tue May 04 10:49:32 2021 -0700
+++ b/relnotes/next	Tue May 04 08:54:28 2021 -0700
@@ -1,5 +1,8 @@
 == New Features ==
- 
+
+ * `hg config` now has a `--source` option to show where each
+   configuration value comes from.
+
 
 == Default Format Change ==