Adding ability to user select separator in config

[emersonbottero]

@JakeHalfpenny , I don't get it how would you tell vitepress to use another separator, because the links are created by vitepress, I'm just following the conventions so my links can match it.

[patarapolw]

Maybe it doesn't make sense to make the key visible, with capitalization and arbitrary hyphenation. (There is already the preexisting hyphens, plus new from slashes.)

https://github.com/emersonbottero/vitepress-plugin-search/blob/aaab0a87516dcd69f6b3e497bf1f8a1d41deb118/src/Search.vue#L167-L176

[emersonbottero]

Could you please try the last version?