Fix #34: Introduce fuzzyLocales option to redirect

[TiEul]

Summary

This change introduces the fuzzyLocales option to the redirect plugin. It allows users to configure the language-based redirects in a way that they only take the language into account while ignoring specific dialects. For example, this means that users with browsers that sendde-AT as a locale will still be forwarded to the de-DE locale, as the plugin will only take the lowercase de into account while ignoring the region-specific uppercase DE and AT. This is only a fallback, so if both exist, users will be forwarded to the appropriate dialect version of their language.

Which package does this PR involve? (check one)

• [ ] root project
• [ ] vuepress-plugin-clean-urls
• [ ] vuepress-plugin-container
• [ ] vuepress-plugin-dehydrate
• [ ] vuepress-plugin-medium-zoom
• [ ] vuepress-plugin-named-chunks
• [ ] vuepress-plugin-nprogress
• [x] vuepress-plugin-redirect
• [ ] vuepress-plugin-smooth-scroll
• [ ] vuepress-plugin-table-of-contents
• [ ] vuepress-plugin-typescript
• [ ] vuepress-plugin-zooming
• [ ] vuepress-mergeable
• [ ] vuepress-types

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix (fix)
• [x] Feature (feat)
• [ ] Performance enhancement (perf)
• [ ] Code Style (style)
• [ ] Refactor (refactor)
• [x] Docs (docs)
• [ ] Build-related changes (build)
• [ ] CI-related changes (ci)
• [ ] Testing (test)
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• [x] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

Other information:

https://github.com/vuepress/vuepress-community/issues/34

[TiEul]

@meteorlxy Let me know if I need to fix anything here or if you have any objections to this PR in general. Just as a note, I actually think the behavior I added should be the default behavior, I merely added the option to turn it off to not cause any backwards-breaking behaviors. Generally, I would assume that choosing the closest fallback language is better than "randomly" choosing English, for example.