assistant2: Add keybinding to toggle `LanguageModelSelector` #37691

Job	Run time
Check Postgres and Protobuf migrations, mergability	13s
Check formatting and spelling	19s
(Linux) Build Remote Server	1m 41s
(Linux) Run Clippy and tests	17m 5s
(macOS) Run Clippy and tests	6m 35s
(Windows) Run Clippy and tests	14m 1s
Create a macOS bundle	0s
Create arm64 Linux bundle	0s
Create a Linux bundle	0s
Auto release preview	0s
	39m 54s

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