[FIX] mail: chatter attachments overflow

Before this PR, posting a message containing an attachment with a long
name in the chatter would result in the chatter overflowing the main
window. This is due to the fact that flex items cannot be smaller than
their content.

This PR fixes the issue by adding the `overflow-auto` class to the
chatter container in order to override the default `min-width: auto`
of flex items thus allowing them to be smaller.

closes odoo/odoo#106892

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/components/chatter_container/chatter_container.xml

@@ -2,7 +2,7 @@
 <templates xml:space="preserve">
 
     <t t-name="mail.ChatterContainer" owl="1">
-        <div class="o_ChatterContainer flex-grow-1 d-flex" t-att-class="{ 'o-isInFormSheetBg mx-auto': props.isInFormSheetBg }" t-attf-class="{{ props.className }}" data-command-category="mail" t-ref="root">
+        <div class="o_ChatterContainer flex-grow-1 d-flex overflow-auto" t-att-class="{ 'o-isInFormSheetBg mx-auto': props.isInFormSheetBg }" t-attf-class="{{ props.className }}" data-command-category="mail" t-ref="root">
             <t t-if="chatter and chatter.thread">
                 <Chatter record="chatter"/>
             </t>