[IMP] developer: improve navigation in top-level pages

Prior to this commit, users had to either know in advance or guess the
location of the content they were looking for. Top-level pages of the
"Developer" section of the documentation, in particular the "Developer"
page itself, were listing their sub-pages without directions for users.

This commit brings the following changes to improve the navigation:
- add directions for users on the "Developer" page and list the three
  main categories of developer documentation ("Tutorials", "How-to
  guides", and "Reference") with explanations of their content and
  target audience;
- add categories for content cards on the "Tutorials" and "How-to
  guides" pages, and fine-tune the toctree of the "Reference" page to
  more easily locate specific topics;
- clarify what are the "Python framework" and the "JavaScript framework"
  by relabelling them to "Server framework" and "Web framework" on
  top-level pages, as some users were confused to find that the JS
  framework was not responsible for the server, and others that the
  documentation for QWeb template is located in the Python documentation;
- extract the "Setup guide" from the "Getting started" tutorial and
  rename the latter to "Server framework 101" to allow reusing the setup
  guide in other tutorials and make clear that the "Server framework 101"
  tutorial is not about the Web framework.

task-3802536

closes odoo/documentation#8597

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>
Co-authored-by: Valeriya (vchu) <vchu@odoo.com>

content/developer/tutorials/pdf_reports.rst

@@ -3,13 +3,11 @@ Build PDF Reports
 =================
 
 .. important::
-   This tutorial is an extension of the :doc:`getting_started` tutorial. Make sure you have
+   This tutorial is an extension of the :doc:`server_framework_101` tutorial. Make sure you have
    completed it and use the `estate` module you have built as a base for the exercises in this
-   tutorial. Fetch the branch `{BRANCH}-core` from the `technical-training-solutions
-   <https://github.com/odoo/technical-training-solutions/tree/{BRANCH}-core>`_ repository if you
-   want to start from a clean base.
+   tutorial.
 
-We were previously :ref:`introduced to QWeb <tutorials/getting_started/15_qwebintro>`
+We were previously :doc:`introduced to QWeb <server_framework_101/14_qwebintro>`
 where it was used to build a kanban view. Now we will expand on one of QWeb's
 other main uses: creating PDF reports. A common business requirement is the ability to create documents
 to send to customers and to use internally. These reports can be used to summarize and display
@@ -180,7 +178,7 @@ Its contents are all explained in :ref:`the documentation <reference/actions/rep
 An ``ir.actions.report`` is primarily used via the Print menu of a model's view. In the practical
 example, the ``binding_model_id`` specifies which model's views the report should show, and Odoo
 will auto-magically add it for you. Another common use case of the report action is to link it to
-a button as we learned in :ref:`tutorials/getting_started/10_actions`. This is handy for reports
+a button as we learned in :doc:`server_framework_101/09_actions`. This is handy for reports
 that only make sense under specific conditions. For example, if we wanted to make a "Final Sale"
 report, then we can link it to a "Print Sale Info" button that appears in the form view only when
 the property is "Sold".