Add chat-specific message search

**Is your feature request related to a problem? Please describe.**
When I already know in which chat I've sent/received a message that I'm looking for, I don't like having to also scroll through messages from other chats to find it.

**Describe the solution you'd like**
A search button in the chat details view that prompts a search bar in the chat view and only searches through the selected chat.

**Describe alternatives you've considered**
Using the current search implementation while being very mildly annoyed.

**Additional context**
I have in mind the Telegram implementation, but other implementations are of course possible (e.g. if I remember correctly, Whatsapp used to have a magnifying glass icon in the top bar).