refactor: rename the application package to docsgpt

The backend import package is now docsgpt, the name it will carry on PyPI;
application was far too generic to install into anyone's site-packages.
git mv plus a mechanical rewrite of every import, dotted string and path
reference: 734 Python files, the compose files, Dockerfile, workflows, docs,
setup scripts, devcontainer, k8s manifests, vscode config, pytest and coverage
config, .gitignore. Behaviour is unchanged.

Kept for one release:
- A top-level application package whose meta-path finder resolves
  application.x.y to the already-imported docsgpt.x.y object, so old imports
  and entry points (celery -A application.app.celery,
  uvicorn application.asgi:asgi_app) keep working with a FutureWarning.
- Celery registers every application.* task name as an alias of its
  docsgpt.* task on start-up, so messages queued by the previous release still
  run. The redbeat key prefix moves to redbeat:docsgpt:v2: so schedule entries
  the previous release wrote are left unread instead of firing twice.

The backend image builds from the repository root (docker build -f
docsgpt/Dockerfile .) so it can ship the alias package; a root .dockerignore
allow-lists docsgpt/ and application/ and keeps caches, local data, .env
files, the sample index files and the Dockerfile out. Compose and the image
workflows point at the new context.

docsgpt/parser/file/json_parser.py

@@ -0,0 +1,57 @@
+import json
+from typing import Any, Dict, List, Union
+from pathlib import Path
+
+from docsgpt.parser.file.base_parser import BaseParser
+
+class JSONParser(BaseParser):
+    r"""JSON (.json) parser.
+
+    Parses JSON files into a list of strings or a concatenated document.
+    It handles both JSON objects (dictionaries) and arrays (lists).
+
+    Args:
+        concat_rows (bool): Whether to concatenate all rows into one document.
+            If set to False, a Document will be created for each item in the JSON.
+            True by default.
+
+        row_joiner (str): Separator to use for joining each row.
+            Only used when `concat_rows=True`.
+            Set to "\n" by default.
+
+        json_config (dict): Options for parsing JSON. Can be used to specify options like
+        custom decoding or formatting. Set to empty dict by default.
+
+    """
+
+    def __init__(
+            self,
+            *args: Any,
+            concat_rows: bool = True,
+            row_joiner: str = "\n",
+            json_config: dict = {},
+            **kwargs: Any
+    ) -> None:
+        """Init params."""
+        super().__init__(*args, **kwargs)
+        self._concat_rows = concat_rows
+        self._row_joiner = row_joiner
+        self._json_config = json_config
+
+    def _init_parser(self) -> Dict:
+        """Init parser."""
+        return {}
+
+    def parse_file(self, file: Path, errors: str = "ignore") -> Union[str, List[str]]:
+        """Parse JSON file."""
+        
+        with open(file, 'r', encoding='utf-8') as f:
+                data = json.load(f, **self._json_config)
+
+        if isinstance(data, dict):
+            data = [data]
+
+        if self._concat_rows:
+            return self._row_joiner.join([str(item) for item in data])
+        else:
+            return data