setup: migrate to mkdocs-material version 5

[mvidalgarcia]

mkdocs-material version 5 has brought many changes but unfortunately is incompatible with our current state of repo.

They have written a nice guide on how to update to version 5.x: https://squidfunk.github.io/mkdocs-material/releases/5/

I followed this step.

diff --git a/mkdocs.yml b/mkdocs.yml
index bf0da72..3835793 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -27,13 +27,13 @@ theme:
 # Customization
 extra:
   social:
-  - type: 'github'
+  - icon: 'fontawesome/brands/github-alt'
     link: 'https://github.com/reanahub'
-  - type: 'twitter'
+  - icon: 'fontawesome/brands/twitter'
     link: 'https://twitter.com/reanahub'
-  - type: 'comments'
+  - icon: 'fontawesome/brands/discourse'
     link: 'https://forum.reana.io'
-  - type: 'globe'
+  - icon: 'fontawesome/solid/globe'
     link: 'http://www.reana.io'
 extra_css:
   - stylesheets/extra.css

That was the only one breaking our build, but still, the appearance doesn't look as what we currently have:

Stuff to adapt/fix:

• Logo dimensions
• Horizontal tab menu missing
• Some blue colored links (see "Welcome" in screenshot)
• Black borders (footer)
• Adapt social icons
• Some of our css customizations are gone (check and cleanup). Take advantage of this to use the brand new css variables For instance, something like the following will convert all the active links into green.

  :root [data-md-color-primary="white"] {
      --md-primary-fg-color: green;
  }

• Etc.

[mvidalgarcia]

Here the diff of ILS documentation upgrade, that might be useful as reference.