feat: create libretime_shared package (#1349)

* feat: create libretime_shared package

- We don't use pydantic.BaseSettings because of some
  incompatble loading behavior.

* fix: whitelist pydantic in pylintrc

* docs: update to new BaseConfig behavior

* docs: change confusing config filepath

shared/libretime_shared/app.py

@@ -0,0 +1,36 @@
+from abc import ABC, abstractmethod
+from os import PathLike
+from pathlib import Path
+from typing import Optional
+
+from loguru import logger
+
+from .logging import LogLevel, setup_logger
+
+
+# pylint: disable=too-few-public-methods
+class AbstractApp(ABC):
+    """
+    Abstracts the creation of an application to reduce boilerplate code such
+    as logging setup.
+    """
+
+    log_level: LogLevel
+
+    @property
+    @abstractmethod
+    def name(self) -> str:
+        ...
+
+    def __init__(
+        self,
+        *,
+        verbosity: int,
+        log_filepath: Optional[PathLike] = None,
+    ):
+        if log_filepath is not None:
+            log_filepath = Path(log_filepath)
+
+        self.log_level = setup_logger(verbosity=verbosity, filepath=log_filepath)
+
+        logger.info(f"Starting {self.name}...")