With this commit, messages can be pinned on a channel and
chat conversation. There's a new menu listing all pinned
messages on a conversation, and we can jump to these messages
in the current conversation.
As this feature incentives to see older messages, this commit
also adds a "Jump to Present" button when looking at old messages.
closesodoo/odoo#116666
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>