adding spack -c to set one off config arguments (#22251)

This pull request will add the ability for a user to add a configuration argument on the fly, on the command line, e.g.,:

```bash
$ spack -c config:install_tree:root:/path/to/config.yaml -c packages:all:compiler:[gcc] list --help
```
The above command doesn't do anything (I'm just getting help for list) but you can imagine having another root of packages, and updating it on the fly for a command (something I'd like to do in the near future!)

I've moved the logic for config_add that used to be in spack/cmd/config.py into spack/config.py proper, and now both the main.py (where spack commands live) and spack/cmd/config.py use these functions. I only needed spack config add, so I didn't move the others. We can move the others if there are also needed in multiple places. 

1 files changed, 1 insertions, 1 deletions

diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index c76eb7d4a8..ef33f0cb9e 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -331,7 +331,7 @@ _spacktivate() {
 _spack() {
     if $list_options
     then
-        SPACK_COMPREPLY="-h --help -H --all-help --color -C --config-scope -d --debug --timestamp --pdb -e --env -D --env-dir -E --no-env --use-env-repo -k --insecure -l --enable-locks -L --disable-locks -m --mock -p --profile --sorted-profile --lines -v --verbose --stacktrace -V --version --print-shell-vars"
+        SPACK_COMPREPLY="-h --help -H --all-help --color -c --config -C --config-scope -d --debug --timestamp --pdb -e --env -D --env-dir -E --no-env --use-env-repo -k --insecure -l --enable-locks -L --disable-locks -m --mock -p --profile --sorted-profile --lines -v --verbose --stacktrace -V --version --print-shell-vars"
     else
         SPACK_COMPREPLY="activate add arch blame build-env buildcache cd checksum ci clean clone commands compiler compilers concretize config containerize create deactivate debug dependencies dependents deprecate dev-build develop docs edit env extensions external fetch find flake8 gc gpg graph help info install license list load location log-parse maintainers mark mirror module patch pkg providers pydoc python reindex remove rm repo resource restage solve spec stage style test test-env tutorial undevelop uninstall unit-test unload url verify versions view"
     fi