[IMP] portal: improve the portal share template

The purpose of the commit is to improve the share template
messaging and ui.

so in this commit did the following changes:
  - In invitation email template made some changes as follows:
    - You have been invited -> Mitchell Admin has invited
    - following document -> following project(record description)

task-2903637

Part-of: odoo/odoo#95971

addons/portal/data/mail_templates.xml

@@ -3,8 +3,9 @@
 
     <template id="portal_share_template">
         <div>
+            <br/>
             <p>Dear <span t-esc="partner.name"/>,</p>
-            <p>You have been invited to access the following document:</p>
+            <p><span t-out="user.name"/> has invited you to access the following <span t-out="model_description"/>:</p>
             <br/>
             <a t-attf-href="#{share_link}" style="background-color: #875A7B; padding: 10px; text-decoration: none; color: #fff; border-radius: 5px; font-size: 12px;"><strong>Open </strong><strong t-esc="record.display_name"/></a><br/>
             <br/>

addons/portal/wizard/portal_share.py

@@ -67,8 +67,9 @@ class PortalShare(models.TransientModel):
             self.resource_ref.message_post_with_source(
                 'portal.portal_share_template',
                 render_values={'partner': partner, 'note': self.note, 'record': self.resource_ref,
-                        'share_link': share_link},
+                        'share_link': share_link,
-                subject=_("You are invited to access %s", self.resource_ref.display_name),
+                        'model_description': self.env['ir.model']._get(self.resource_ref._name).display_name.lower()},
+                subject=_("Invitation to access %s", self.resource_ref.display_name),
                 subtype_xmlid='mail.mt_note',
                 email_layout_xmlid='mail.mail_notification_light',
                 partner_ids=partner.ids)
@@ -86,8 +87,9 @@ class PortalShare(models.TransientModel):
             self.resource_ref.message_post_with_source(
                 'portal.portal_share_template',
                 render_values={'partner': partner, 'note': self.note, 'record': self.resource_ref,
-                        'share_link': share_link},
+                        'share_link': share_link,
-                subject=_("You are invited to access %s", self.resource_ref.display_name),
+                        'model_description': self.env['ir.model']._get(self.resource_ref._name).display_name.lower()},
+                subject=_("Invitation to access %s", self.resource_ref.display_name),
                 subtype_xmlid='mail.mt_note',
                 email_layout_xmlid='mail.mail_notification_light',
                 partner_ids=partner.ids)