allow symbolic links to be followed during autoimport (#4268)

## What type of PR is this? (check all applicable)

- [X] Feature
- [X] Bug Fix

## Have you discussed this change with the InvokeAI team?
- [X] Yes

## Have you updated all relevant documentation?
- [X] Yes

## Description

Follow symbolic links when auto importing from a directory. Previously
links to files worked, but links to directories weren’t entered during
the scanning/import process.

invokeai/backend/install/migrate_to_3.py

@@ -116,7 +116,7 @@ class MigrateTo3(object):
         appropriate location within the destination models directory.
         """
         directories_scanned = set()
-        for root, dirs, files in os.walk(src_dir):
+        for root, dirs, files in os.walk(src_dir, followlinks=True):
             for d in dirs:
                 try:
                     model = Path(root, d)

invokeai/backend/model_management/model_search.py

@@ -56,7 +56,7 @@ class ModelSearch(ABC):
         self.on_search_completed()
 
     def walk_directory(self, path: Path):
-        for root, dirs, files in os.walk(path):
+        for root, dirs, files in os.walk(path, followlinks=True):
             if str(Path(root).name).startswith("."):
                 self._pruned_paths.add(root)
             if any([Path(root).is_relative_to(x) for x in self._pruned_paths]):

invokeai/backend/stable_diffusion/image_degradation/utils_image.py

@@ -89,7 +89,7 @@ def get_image_paths(dataroot):
 def _get_paths_from_images(path):
     assert os.path.isdir(path), "{:s} is not a valid directory".format(path)
     images = []
-    for dirpath, _, fnames in sorted(os.walk(path)):
+    for dirpath, _, fnames in sorted(os.walk(path, followlinks=True)):
         for fname in sorted(fnames):
             if is_image_file(fname):
                 img_path = os.path.join(dirpath, fname)