Revert "feat: remove unmaintened modules (#443)"

This reverts commit b1434e34d0.

attachment_s3/README.rst

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+Attachments on S3 storage
+=========================
+
+This addon allows to store the attachments (documents and assets) on S3 or any
+other S3-compatible Object Storage.
+
+Configuration
+-------------
+
+Activate S3 storage:
+
+* Create or set the system parameter with the key ``ir_attachment.location``
+  and the value in the form ``s3``.
+
+Configure accesses with environment variables:
+
+* ``AWS_HOST`` (not required if using AWS services)
+* ``AWS_REGION`` (required if using AWS services)
+* ``AWS_ACCESS_KEY_ID``
+* ``AWS_SECRET_ACCESS_KEY``
+* ``AWS_BUCKETNAME`` (optional {db} placeholder)
+
+Read-only mode:
+
+The bucket and the file key are stored in the attachment. So if you change the
+``AWS_BUCKETNAME`` or the ``ir_attachment.location``, the existing attachments
+will still be read on their former bucket. But as soon as they are written over
+or new attachments are created, they will be created on the new bucket or on
+the other location (db or filesystem). This is a convenient way to be able to
+read the production attachments on a replication (since you have the
+credentials) without any risk to alter the production data.
+
+This addon must be added in the server wide addons with (``--load`` option):
+
+``--load=web,attachment_s3``
+
+The System Parameter ``ir_attachment.storage.force.database`` can be customized to
+force storage of files in the database. See the documentation of the module
+``base_attachment_object_storage``.
+
+Multi-tenancy
+-------------
+
+Use the `{db}` placeholder to handle multi-tenancy.
+
+On instances that hold multiple databases, it's preferable to have one bucket per database.
+
+To handle this, you can insert the `{db}` placeholder in your bucket name variable ``AWS_BUCKETNAME``.
+It will be replaced by the database name.
+This will give you a unique bucketname per database.
+
+
+Limitations
+-----------
+
+* You need to call ``env['ir.attachment'].force_storage()`` after
+  having changed the ``ir_attachment.location`` configuration in order to
+  migrate the existing attachments to S3.