[add] Predicate as `telega-chat-send-message-on-ret'

Make it possible to use custom predicate to decide what should RET do

Fixes #465

telega-chat.el

@@ -4499,9 +4499,10 @@ Behaviour depends on point position and value for
 `telega-chat-send-message-on-ret'."
   (interactive)
   (if (or (eq 'always telega-chat-send-message-on-ret)
-          (eobp)                        ;point at the end of the prompt
-          (and (eq 'if-at-the-end-or-C-u telega-chat-send-message-on-ret)
-               current-prefix-arg))
+          (and (eq 'if-at-the-end telega-chat-send-message-on-ret)
+               (eobp))
+          (and (functionp telega-chat-send-message-on-ret)
+               (funcall telega-chat-send-message-on-ret)))
       (call-interactively #'telega-chatbuf-input-send)
     (call-interactively #'newline)))
 

telega-customize.el

@@ -1309,10 +1309,11 @@ Increasing this limit increases number of events telega needs to process."
   "Customization for `\\<telega-chat-mode-map>\\[telega-chatbuf-newline-or-input-send]' behaviour."
   :type '(choice
           (const :tag "Always send a message" always)
+          ;; NOTE: `if-at-the-end' is the same as #'eobp predicate
           (const :tag "Send message if point at the end of prompt" if-at-the-end)
-          (const :tag "Send message if C-u is specified \
-or point at the end of prompt" if-at-the-end-or-C-u))
-  :package-version '(telega . "0.8.121")
+          (function :tag "Predicate returning non-nil to send input"))
+  :package-version '(telega . "0.8.254")
+  :options '(eobp)
   :group 'telega-chat)
 
 (defcustom telega-chat-send-messages-async nil