[REF] install: move intro to main install page and split by install type

This PR moves the introduction about the different installation methods and editions found on the
install/install.rst page directly under the main install/ page. It creates three pages, one per
installation method documented on the install/install.rst page (Docker being documented on
docker.com and maintained by us), and moves the related content there. In addition, it fixes various
typos/grammar issues and improves the content according to the documentation guidelines. Various
references and links across the documentation had to be fixed accordingly.

task-3459070

closes odoo/documentation#5539

X-original-commit: da2a48b9fd
Signed-off-by: Xavier Platteau (xpl) <xpl@odoo.com>

content/administration/maintain/enterprise.rst

@@ -61,7 +61,7 @@ have your own favourite. You may need to adapt sections to your usual workflow.
 
 * Shutdown your server
 * Backup your community database
-* Update the ``--addons-path`` parameter of your launch command (see :ref:`setup/install/source`)
+* Update the ``--addons-path`` parameter of your launch command (see :doc:`../install/source`)
 * Install the web_enterprise module by using
 
   .. code-block:: console

content/administration/maintain/update.rst

@@ -46,7 +46,7 @@ Updating Odoo is accomplished by simply reinstalling the latest version of your
 Edition on top of your current installation. This will preserve your data without any alteration,
 as long as you do not uninstall PostgreSQL (the database engine that comes with Odoo).
 
-The main reference for updating is logically our :ref:`installation guide <setup/install>`,
+The main reference for updating is logically our :doc:`installation guide <../install>`,
 which explains the common installation methods.
 
 Updating is also most appropriately accomplished by the person who deployed Odoo initially,