Speed up the build of the website

Originally created by @sajolida on #11151 (Redmine)

As suggested in #11135 (comment 62484) we could measure the time to build the wiki in the past (without the Installation Assistant for example) and now, and try to set a realistic goal.

Then we should investigate on concrete changes to speed things up, like #11135 (closed).

Subtasks

• #10792 (closed)
• #11135 (closed)
• #11156 (closed)
• #11158 (closed)
• #11227 (closed)
• #11249 (closed)

Related issues

• Related to #9323 (closed)