Support Beamer logo graphic options

[sidneymau]

Describe your proposed improvement and the problem it solves.

It would be convenient to be able to specify options for the included logo graphic in beamer (similar to what was done for the title graphic with #9207). Because the logo is passed directly to \includegraphics in the same way as the titlegraphic, the same solution could apply here (cf.

pandoc/data/templates/default.beamer

Lines 121 to 129 in e9ec0c5

	$if(titlegraphic)$
	\titlegraphic{
	$for(titlegraphic)$
	\includegraphics$if(titlegraphicoptions)$[$for(titlegraphicoptions)$$titlegraphicoptions$$sep$, $endfor$]$endif${$titlegraphic$}$sep$\enspace
	$endfor$}
	$endif$
	$if(logo)$
	\logo{\includegraphics{$logo$}}
	$endif$

).

Describe alternatives you've considered.

The only alternative I think would be to manually change the logo image (e.g., making a smaller PDF) or to use header-includes

[sidneymau]

I think the change would be

$if(logo)$
\logo{\includegraphics$if(logooptions)$[$logooptions$]$endif${$logo$}}
$endif$

since the logo is singular, there would be no iteration. Happy to open a PR if this seems reasonable

[jgm]

Sure, go ahead. Don't forget to update the portion of the manual where beamer-relevant variables are described.