Improve content discovery

[Kostov6]

What would you like to be added:
By improving document titles and descriptions we gain the following:

• better search because they can represent content's keywords better and have a higher weight when evaluating search score
• section pages will have more utility because through them the page description is seen. This will stimulate sections to be written with meaningful content. This will improve content read flow and discovery - if the search function does not find the needed content one can just browse through the sections to find it

Gardener changes:

• Adding descriptions and titles on user documents (1/3) gardener#10077
• Move usage content into a designated place (2/3) gardener#10436
• Content related changes - split document to new ones for dedicated personas.
• Improve glossary page