Per-user settings such as sync.smartsync live in ~/.repoconfig/config,
but reading or changing them required knowing the file location and
running `git config --file ~/.repoconfig/config ...`.
Add `repo config` as a thin wrapper around RepoConfig.ForUser(),
following the subcommand style of modern `git config`:
* `repo config get <name>` prints the value(s), exiting 1 if unset.
* `repo config set <name> <value>` sets it.
* `repo config unset <name>` removes it; a missing key is a no-op.
* `repo config list` shows all settings.
Values are stored as strings; `--type=bool|int` validates and
canonicalizes them on set and get, like `git config --type`. `-z` makes
get and list NUL-terminated for scripting. Setting names are validated
by `git config` itself when writing.
Factor the value parsing out of GitConfig.GetBoolean()/GetInt() into
ParseBoolean()/ParseInt() so the command and the readers agree, and
accept on/off/1/0 as booleans like git does.
Only the per-user file is handled; per-checkout settings in
.repo/manifests.git/config are out of scope. Like other subcommands, it
runs from inside a repo checkout.
Update docs/repoconfig.md to use the new command in its examples and
add zsh completion and the man page.
Bug: 569927750
Test: ./run_tests
Change-Id: I940d0318549fe9d79f6f9173139f0b96a706f1bf
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/645727
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Insaf Latypov <saferif@google.com>
Commit-Queue: Insaf Latypov <saferif@google.com>
