IBX-9609: Upgrade mkdocs (#2627)

* requirements.txt: Upgrade mkdocs to latest
* requirements.txt: Upgrade Markdown to latest
* requirements.txt: Upgrade Pygments to latest
* requirements.txt: Upgrade PyMdown Extensions to latest
* requirements.txt: Upgrade Material for MkDocs to latest
* requirements.txt: Upgrade Mkdocs-Macros to latest
* requirements.txt: Upgrade mkdocs-redirects to latest
* requirements.txt: Upgrade MkDocs Autolinks Plugin to latest
* navigation.css: Fix right ToC (probably due to Material for MkDocs upgrade)
* navigation.css: Fix left ToC (probably due to Material for MkDocs upgrade)
* .readthedocs.yml: Upgrade python & pip (#2653)
* mkdocs: `absolute_links: relative_to_docs`

(cherry picked from commit 97cf2cc)

Author: adriendupuis

mkdocs.yml

@@ -947,7 +947,7 @@ extra:
   latest_tag_4_3: '4.3.5'
   latest_tag_4_4: '4.4.4'
   latest_tag_4_5: '4.5.7'
-  latest_tag_4_6: '4.6.17'
+  latest_tag_4_6: '4.6.18'
 
   symfony_doc: 'https://symfony.com/doc/5.x'
   user_doc: 'https://doc.ibexa.co/projects/userguide/en/master'