Always allow to join conversation in sidebar even with no shares

Is your feature request related to a problem? Please describe.
Having to share first before joining a conversation feels like an extra burden.
Some people like me (who like monologuing) would like to create a conversation before sharing with other people.

Describe the solution you'd like
Instead of showing "please share this file first" in the conversation tab in the sidebar, allow creating a conversation right away.
Then inside the newly created chat, we could add an extra message "you are alone in this conversation, please share the file to invite more people" or something alike.

Additional context
Would also make it faster to test as it doesn't require to share first.
Would obsolete the issue about the conversation tab not updating after sharing.

Even cooler would be if I could create shares from within the conversation: if I ping someone then I'd be asked "this person doesn't have access to this file, do you want to share it with them ?"

@nextcloud/designers-talk

Start by locating the sidebar conversation tab and reproduce its current no-share state, where it shows "please share this file first." Define the initial conversation flow and the message shown when nobody else has access, then verify the sidebar and newly created chat behave consistently. The proposed in-chat sharing prompt is a separate, broader scope to assess.