feat: Allow modifying docs url prefix (#914)

* Allow other routes than /docs in the URL

siteConfig.js has a new mandatory field named *docsRoute* which default
value is 'docs' and that can be customized by the user.

This change will allow users who uses the library to host guides and
tutorials to customize their websites by assign 'docsRoute' values
like 'tutorials' or 'guides'.

Fixes #879

* Make "docsRoute" field optional

* Isolate docsRoute login in getDocsRoute function

* Rename docsRoute to docsUrl

* Run prettier

* Remove old folders

* fix: Restore docusaurus reference link

* fix: Add `docsUrl` param fallback. Refactor multiple function calls

* Fix linting errors

* Update description for docsUrl field

* Reduce redundant calls to getDocsUrl

* Replace a missed use case for `docsUrl` instead of the function call

* Move `getDocsUrl` out from `server/routing.js` to `server/utils.js`

**Why?**
Because `routing.js` is exporting all router RegEx's, and the
`getDocsUrl` suffices more as a util

* WiP: Align leading slashes and fix routing around `docsUrl`

Checklist:
- [x] Added `removeDuplicateLeadingSlashes` util to make sure there is only
one leading slash
- [-] Fix edge cases for routing:
  - [x] `docsUrl: ''`
  - [ ] `docsUrl: '/'`
  - [ ] make it work with languages
  - [ ] make it work with versioning

* Make leading slashes canonical cross routing and generated links

This ensures correct routing for customized `baseUrl` and `docsUrl`.

- Changed all routing functions to take `siteConfig` instead of
`siteConfig.baseUrl`
- Updated tests accordingly

* Alternative fallback for `docsUrl`

* rework/ fix implementation

* cleanup

* refactor and add docs for config props

* fix typo

* fix broken url

v1/lib/server/versionFallback.js

@@ -14,8 +14,9 @@ const metadataUtils = require('./metadataUtils');
 
 const env = require('./env.js');
 const utils = require('./utils.js');
+const loadConfig = require('./config');
 
-const siteConfig = require(`${CWD}/siteConfig.js`);
+const siteConfig = loadConfig(`${CWD}/siteConfig.js`);
 
 const ENABLE_TRANSLATION = fs.existsSync(`${CWD}/languages.js`);
 
@@ -187,14 +188,16 @@ function processVersionMetadata(file, version, useVersion, language) {
 
   const latestVersion = versions[0];
 
+  const docsPart = `${siteConfig.docsUrl ? `${siteConfig.docsUrl}/` : ''}`;
+  const versionPart = `${version !== latestVersion ? `${version}/` : ''}`;
   if (!ENABLE_TRANSLATION && !siteConfig.useEnglishUrl) {
-    metadata.permalink = `docs/${
-      version !== latestVersion ? `${version}/` : ''
-    }${metadata.original_id}.html`;
+    metadata.permalink = `${docsPart}${versionPart}${
+      metadata.original_id
+    }.html`;
   } else {
-    metadata.permalink = `docs/${language}/${
-      version !== latestVersion ? `${version}/` : ''
-    }${metadata.original_id}.html`;
+    metadata.permalink = `${docsPart}${language}/${versionPart}${
+      metadata.original_id
+    }.html`;
   }
   metadata.id = metadata.id.replace(
     `version-${useVersion}-`,