find: deprecate spack find -bootstrap for spack -bootstrap find (#29152)

Since adding the `spack --bootstrap` argument we don't need `spack find --bootstrap`
anymore.  Deprecate it.

lib/spack/spack/cmd/find.py

@@ -202,6 +202,12 @@ def display_env(env, args, decorator):
 
 
 def find(parser, args):
+    if args.bootstrap:
+        tty.warn(
+            "`spack find --bootstrap` is deprecated and will be removed in v0.19.",
+            "Use `spack --bootstrap find` instead."
+        )
+
     if args.bootstrap:
         bootstrap_store_path = spack.bootstrap.store_path()
         with spack.bootstrap.ensure_bootstrap_configuration():

lib/spack/spack/test/cmd/find.py

@@ -333,3 +333,8 @@ def test_find_loaded(database, working_env):
     output = find('--loaded')
     expected = find()
     assert output == expected
+
+
+def test_bootstrap_deprecated():
+    output = find('--bootstrap')
+    assert "`spack find --bootstrap` is deprecated" in output