Strip whitespace from model URLs (#4863)

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

- [ ] Refactor
- [ ] Feature
- [X] Bug Fix
- [ ] Optimization
- [ ] Documentation Update
- [ ] Community Node Submission


## Have you discussed this change with the InvokeAI team?
- [X] Yes
- [ ] No, because:

      
## Have you updated all relevant documentation?
- [X] Yes
- [ ] No


## Description

This PR strips leading and trailing whitespace from URLs that are
entered into either the Web Model Manager import field, or using the
TUI.

## Related Tickets & Documents

Closes #4536


## QA Instructions, Screenshots, Recordings

Try to import a URL with leading or trailing whitespace. Should not work
in current main. This PR should fix it.

invokeai/app/api/routers/models.py

@@ -152,6 +152,7 @@ async def import_model(
 ) -> ImportModelResponse:
     """Add a model using its local path, repo_id, or remote URL. Model characteristics will be probed and configured automatically"""
 
+    location = location.strip("\"' ")
     items_to_import = {location}
     prediction_types = {x.value: x for x in SchedulerPredictionType}
     logger = ApiDependencies.invoker.services.logger

invokeai/backend/install/model_install_backend.py

@@ -236,9 +236,16 @@ class ModelInstall(object):
         if not models_installed:
             models_installed = dict()
 
+        model_path_id_or_url = str(model_path_id_or_url).strip("\"' ")
+
         # A little hack to allow nested routines to retrieve info on the requested ID
         self.current_id = model_path_id_or_url
         path = Path(model_path_id_or_url)
+
+        # fix relative paths
+        if path.exists() and not path.is_absolute():
+            path = path.absolute()  # make relative to current WD
+
         # checkpoint file, or similar
         if path.is_file():
             models_installed.update({str(path): self._install_path(path)})