[MOV] documentation structure reorganization

This commit aims to improve the documentation's navigability by
redefining some categories' purposes and titles.

There is a redirection rule for each documentation page moved.
This ensures that users won't have a 404 error message.

task-3217827

closes odoo/documentation#8063

Signed-off-by: Jonathan Castillo (jcs) <jcs@odoo.com>

content/applications/studio.rst

@@ -0,0 +1,31 @@
+:show-content:
+:hide-page-toc:
+
+======
+Studio
+======
+
+.. toctree::
+   :titlesonly:
+
+   studio/fields
+   studio/views
+   studio/models_modules_apps
+   studio/automated_actions
+   studio/pdf_reports
+
+Studio is a toolbox that allows you to customize Odoo without coding knowledge. For example, you
+can, on any app, add or modify:
+
+- :doc:`Fields <studio/fields>`
+- :doc:`Views <studio/views>`
+- :doc:`Models <studio/models_modules_apps>`
+- :doc:`Automated actions <studio/automated_actions>`
+- :doc:`PDF reports <studio/pdf_reports>`
+- Approval rules
+- Security rules
+
+Or you can :doc:`build an app from scratch <studio/models_modules_apps>`.
+
+.. seealso::
+   - `Odoo Tutorials: Studio <https://www.odoo.com/slides/studio-31>`_