[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/install.rst

@@ -1,14 +1,49 @@
-:nosearch:
+:show-content:
 
 =======
 Install
 =======
 
-.. If you add content on this page, remove the redirect rule 'install -> install/install'
+Depending on the intended use case, there are multiple ways to install Odoo - or not install it at
+all.
+
+- :doc:`Online <install/online>` is the easiest way to use Odoo in production or to try it.
+
+- :doc:`Packaged installers <install/packages>` are suitable for testing Odoo and developing
+  modules. They can be used for long-term production with additional deployment and maintenance
+  work.
+
+- :doc:`Source install <install/source>` provides greater flexibility, as it allows, for example,
+  running multiple Odoo versions on the same system. It is adequate to develop modules and can be
+  used as a base for production deployment.
+
+- A `Docker <https://hub.docker.com/_/odoo/>`_ base image is available for development or
+  deployment.
+
+.. _install/editions:
+
+Editions
+========
+
+There are two different editions.
+
+**Odoo Community** is the free and open-source version of the software, licensed under the `GNU
+LGPLv3 <https://github.com/odoo/odoo/blob/master/LICENSE>`_. It is the core upon which Odoo
+Enterprise is built.
+
+**Odoo Enterprise** is the shared source version of the software, giving access to more
+functionalities, including functional support, upgrades, and hosting. `Pricing
+<https://www.odoo.com/pricing-plan>`_ starts from one app free.
+
+.. tip::
+   :doc:`Switch from Community to Enterprise <maintain/enterprise>` at any time (except for the
+   source install).
 
 .. toctree::
 
-    install/install
-    install/deploy
-    install/cdn
-    install/email_gateway
+   install/online
+   install/packages
+   install/source
+   install/deploy
+   install/cdn
+   install/email_gateway