Add LightningLite to top level imports (#15502)

Co-authored-by: Jirka Borovec <6035284+Borda@users.noreply.github.com>
Co-authored-by: Carlos Mocholí <carlossmocholi@gmail.com>
(cherry picked from commit c32c435)

.github/workflows/ci-pkg-install.yml

@@ -62,6 +62,8 @@ jobs:
         run: python -m lightning --version
 
       - name: DocTest package
+        env:
+          PY_IGNORE_IMPORTMISMATCH: 1
         run: |
           PKG_NAME=$(python -c "print({'app': 'lightning_app', 'lite': 'lightning_lite', 'pytorch': 'pytorch_lightning', 'lightning': 'lightning'}['${{matrix.pkg-name}}'])")
           python -m pytest src/${PKG_NAME} --ignore-glob="**/cli/*-template/**"

src/lightning/__init__.py

@@ -36,6 +36,7 @@ def _detail(self: Any, message: str, *args: Any, **kwargs: Any) -> None:
 from lightning.app.perf import pdb  # noqa: E402
 from lightning.app.utilities.packaging.build_config import BuildConfig  # noqa: E402
 from lightning.app.utilities.packaging.cloud_compute import CloudCompute  # noqa: E402
+from lightning.lite.lite import LightningLite  # noqa: E402
 from lightning.pytorch.callbacks import Callback  # noqa: E402
 from lightning.pytorch.core import LightningDataModule, LightningModule  # noqa: E402
 from lightning.pytorch.trainer import Trainer  # noqa: E402
@@ -59,6 +60,7 @@ def _detail(self: Any, message: str, *args: Any, **kwargs: Any) -> None:
     "LightningModule",
     "Callback",
     "seed_everything",
+    "LightningLite",
     "storage",
     "pdb",
 ]