Feature: Support file type messages on widget and dashboard (#659)

- Adds support for file upload

Co-authored-by: Pranav Raj Sreepuram <pranavrajs@gmail.com>
Co-authored-by: Sojan <sojan@pepalo.com>

app/javascript/dashboard/i18n/locale/en/conversation.json

@@ -9,6 +9,7 @@
     "CLICK_HERE": "Click here",
     "LOADING_INBOXES": "Loading inboxes",
     "LOADING_CONVERSATIONS": "Loading Conversations",
+    "DOWNLOAD": "Download",
     "HEADER": {
       "RESOLVE_ACTION": "Resolve",
       "REOPEN_ACTION": "Reopen",