[ENH][UX] quick_search_mod: Display processing message while the query is being processed

This is the follow up to this MR !4313 (merged). Enhance the quick search module by :

• disabling the submit button when the user submit the query.
• display a Processing message to the user so he knows that the query is being processed.
• And finally enable the submit button for future queries, Once the request has been processed and the results displayed.

• Related Task

Notice, for forum_post object, I notice that some are returning empty <span></span> tags instead of the item link, which causes some bad experience when searching using the quick_search module.

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