Add UI configuration option for stripping trailing slashes from result links

[paulrudy]

I'd like to suggest a Pagefind UI configuration option to strip trailing slashes in Pagefind results.

I understand that this can be done by passing a function to Pagefind's processResult config option as Astro's Starlight does.

But I think it might be useful enough, to enough people, to have as a standalone configuration option.

[shishkin]

Or alternatively, it can be an option for the indexer API.