Fix degrade in speed of indexing large files. Improve summarization

Adding files to the DB for summarization was slow, buggy in two ways:
- We were updating same text of modified files in DB = no of chunks
  per file times

- The `" ".join(file_content)' code was breaking each character in the
  file content by a space. This formats the original file content
  incorrectly before storing in the DB

Because this code ran in the main file indexing path, it was slowing down
file indexing. Knowledge bases with larger files were impacted more strongly

src/khoj/database/adapters/__init__.py

@@ -956,7 +956,7 @@ class FileObjectAdapters:
         return FileObject.objects.create(user=user, file_name=file_name, raw_text=raw_text)
 
     @staticmethod
-    def get_file_objects_by_name(user: KhojUser, file_name: str):
+    def get_file_object_by_name(user: KhojUser, file_name: str):
         return FileObject.objects.filter(user=user, file_name=file_name).first()
 
     @staticmethod

src/khoj/processor/content/text_to_entries.py

@@ -124,7 +124,7 @@ class TextToEntries(ABC):
         deletion_filenames: Set[str] = None,
         user: KhojUser = None,
         regenerate: bool = False,
-        file_to_text_map: dict[str, List[str]] = None,
+        file_to_text_map: dict[str, str] = None,
     ):
         with timer("Constructed current entry hashes in", logger):
             hashes_by_file = dict[str, set[str]]()
@@ -192,16 +192,17 @@ class TextToEntries(ABC):
             logger.debug(f"Added {len(added_entries)} {file_type} entries to database")
 
         if file_to_text_map:
-            # get the list of file_names using added_entries
-            filenames_to_update = [entry.file_path for entry in added_entries]
-            # for each file_name in filenames_to_update, try getting the file object and updating raw_text and if it fails create a new file object
-            for file_name in filenames_to_update:
-                raw_text = " ".join(file_to_text_map[file_name])
-                file_object = FileObjectAdapters.get_file_objects_by_name(user, file_name)
-                if file_object:
-                    FileObjectAdapters.update_raw_text(file_object, raw_text)
-                else:
-                    FileObjectAdapters.create_file_object(user, file_name, raw_text)
+            with timer("Indexed text of modified file in", logger):
+                # get the set of modified files from added_entries
+                modified_files = {entry.file_path for entry in added_entries}
+                # create or update text of each updated file indexed on DB
+                for modified_file in modified_files:
+                    raw_text = file_to_text_map[modified_file]
+                    file_object = FileObjectAdapters.get_file_object_by_name(user, modified_file)
+                    if file_object:
+                        FileObjectAdapters.update_raw_text(file_object, raw_text)
+                    else:
+                        FileObjectAdapters.create_file_object(user, modified_file, raw_text)
 
         new_dates = []
         with timer("Indexed dates from added entries in", logger):