Future 1/n: package in src/ folder (#13293)

* move: pytorch_lightning >> src/

* update setup & install

* update CI

* ci

* update CI for examples

* Self review

* mypy

Co-authored-by: Carlos Mocholí <[email protected]>

* ci

* make

* docs

* typo

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* ci: gpu

* .

* hpu

* typing

* docs

* tpu

Co-authored-by: Carlos Mocholí <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>