ENH: Add option for `bold_column_headers` to `to_latex()`

[mosc9575]

In the latest pandas version 1.4.2 there exists an option to enable bold rows but there isn't a similar option to do the same for the columns. It is something some users on SO were asking for and it seems very logical.

The example from the official documentation with bold_rows=True and bold_column_headers=True should lead to the following example.

import pandas as pd

df = pd.DataFrame(
    dict(name=['Raphael', 'Donatello'],
         mask=['red', 'purple'],
         weapon=['sai', 'bo staff']
        )
)
result= df.to_latex(bold_rows=True, bold_column_headers=True)

>>> result
\begin{tabular}{llll}
\toprule
{} &       \textbf{name} &    \textbf{mask} &    \textbf{weapon} \\
\midrule
\textbf{0} &    Raphael &     red &       sai \\
\textbf{1} &  Donatello &  purple &  bo staff \\
\bottomrule
\end{tabular}

[attack68]

this is currently possibly with Styler.

df.style.applymap_index(lambda v: "font-weight: bold;", axis="columns").to_latex(convert_css=True)

or

df.style.applymap_index(lambda v: "textbf:--rwrap;", axis="columns").to_latex()

or

df.style.applymap_index(lambda v: "bfseries:;", axis="columns").to_latex()

The medium term objective is for the Styler implementation, which is much more flexible, will replace the DataFrame LaTeX formatter.

[jreback]

@attack68 maybe worth adding this to the docs somewhere and closing this

[attack68]

@jreback I have docs and and WIP PR for DataFrame.to_latex ready for this but it relies on #45288, which is in-limbo. Would appreciate your second look that one, and either we close or find some agreement forward, then I can resolve other PRs.