Add option to gatsby-plugin-page-creator to provide my own slugs/slugify function

[iffjey]

Hi again!

So, I'm currently migrating a company blog from Rails to Gatsby, and I'm really enjoying this process, but there is an issue that's blocking me from going LIVE.

All slugs for blog posts are just folder names e.g. /posts/some-cool-article. And we really want to preserve this way of creating slugs. But during migration I found out that gatsby-plugin-page-creator is using Sindre's slugify library. It's a cool library, but it messing with my "unconventional slugs" e.g. /posts/some_very_very-cool-article. So instead of some_very_very-cool-article it become some-very-very-cool-article. I think it should be possible to preserve my own slugs, but it seems like it's impossible now. Otherwise we would need to add a ton of redirects to preserve old links, I don't think that it's a right way.

I think it's a very small but crucial change. We can just add property to gatsby-plugin-page-creator that disables slugify function at all (and just using provided input). Or make possible to provide my own slugify function.

Thanks in advance. I would really appreciate to have some answer from Gatsby core team about this issue. Because last time I was completely ignored even with upvotes :(

Link to previous discussion: #32820