To latex position
- [ ] closes #35281 
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @WillAyd , thanks for the review ! 

I did the changes you asked for, but one test seems to have failed, I'm not sure it's related to what I've written

Would you also want tests when the caption, the label and the position is given ? Just restarted the failure let's see @toobaz @toobaz I tried to match the two functions `_write_table_begin` and `_write_longtable_begin`, but I don't think there is a need for the `_table_float` here, because:
- There is no change in the begin line: whether or not a caption, label or position is given, it will always be `\begin{longtable}...`
- The only difference would be for the line `buf.write("\\\\\n")` but here again the `_table_float` argument is not relevant because this behaviour is needed when a caption or a label is provided, but if only the position would be given it shouldn't be needed > I tried to match the two functions

My suggestion was actually to entirely suppress ``_write_longtable_begin``, given that the only implications of ``longtable=True`` are that the float must be produced, and that its environment name must be ``longtable`` rather than ``table``: all the rest is the same as ``_write_tabular_begin`` (same for ``*_end``).

But this is not a strict necessity, at least in this PR. So if you prefer we can merge this PR after solving my last comment above. > My suggestion was actually to entirely suppress `_write_longtable_begin`

OK @toobaz I hadn't understood ! I tried doing something to resolve this, but I suggest doing it on a separate PR because I think it will get a bit messy.

This work is currently on a [branch of mine](https://github.com/SylvainLan/pandas/blob/merge_table_longtable/pandas/io/formats/latex.py) and we can look at it once this PR is merged
 Looks ready to merge to me. @WillAyd any idea on the two checks still failing? > Looks ready to merge to me. @WillAyd any idea on the two checks still failing?

see #35481. there are 20 fails here, should be only 4 now with lastest numpy-dev Thanks @SylvainLan 