find: add `--hashes` shortcut for piping to other commands (#38663)

People frequently ask us how to pipe `spack find` output to other commands, and we tell
them to do things like this:

```console
$ spack find --format "/{hash}" | spack uninstall -ay
```

Sometimes users don't know about hash references and come up with potentially ambiguous
formulations like this:

```console
spack find --format {name}@{version}%{compiler} | spack uninstall -ay
```

Since this is a common enough thing to want to do, and to make it more obvious how, this
PR adds a `-H` / `--hashes` as a shortcut, so you can now just do:

```console
spack find -H | spack uninstall -ay
```

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/spack/spack/cmd/find.py b/lib/spack/spack/cmd/find.py
index f7bd56db19..15ea5c7709 100644
--- a/lib/spack/spack/cmd/find.py
+++ b/lib/spack/spack/cmd/find.py
@@ -31,6 +31,14 @@ def setup_parser(subparser):
         help="output specs with the specified format string",
     )
     format_group.add_argument(
+        "-H",
+        "--hashes",
+        action="store_const",
+        dest="format",
+        const="{/hash}",
+        help="same as '--format {/hash}'; use with xargs or $()",
+    )
+    format_group.add_argument(
         "--json",
         action="store_true",
         default=False,