building docs to pdf

Nobody has claimed this yet.

### Bug description

I wanted to read the latest docs offline and find/build a pdf of the docs.
On an MBP M1, I did `brew install sphinx`, then `cd docs/` then `pip install -r requirements.txt` which all completed successfully.

No `make` command appears to run without error however.

### What version are you seeing the problem on?

latest

### How to reproduce the bug

try to produce docs without error using

make text
make singlehtml
make latexpdf
make latexpdfja

### Error messages and logs

For example, `make singlehtml` yields a lot of output then finally:

```
FileNotFoundError: [Errno 2] No such file or directory: 'katex'

Exception occurred:
File "/Users/aaelony/mambaforge/envs/py39tt/lib/python3.9/subprocess.py", line 1821, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'katex'
The full traceback has been saved in /var/folders/jc/5gc6fmf52cv6r88m6snhvvlr0000gn/T/sphinx-err-417jlpa9.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at . Thanks!
```
[make--latexpdf.log](https://github.com/Lightning-AI/lightning/files/11181605/make--latexpdf.log)

[make--singlehtml.log](https://github.com/Lightning-AI/lightning/files/11181611/make--singlehtml.log)

### Environment

Current environment

```
#- Lightning Component (e.g. Trainer, LightningModule, LightningApp, LightningWork, LightningFlow):
#- PyTorch Lightning Version (e.g., 1.5.0):
#- Lightning App Version (e.g., 0.5.2):
#- PyTorch Version (e.g., 2.0):
#- Python version (e.g., 3.9):
#- OS (e.g., Linux):
#- CUDA/cuDNN version:
#- GPU models and configuration:
#- How you installed Lightning(`conda`, `pip`, source):
#- Running environment of LightningApp (e.g. local, cloud):
```

Thanks in advance.

cc @borda

Start in docs/ with requirements.txt and the Makefile targets named in the report: text, singlehtml, latexpdf, and latexpdfja. Reproduce the builds, inspect the reported missing katex error and attached logs, then verify that the documentation targets complete without errors on the reported environment.

Written by the indexing model from the issue text.