extensions_ui: Show an error toast when a dev extension fails to install #39329

Job	Run time
Check Postgres and Protobuf migrations, mergability	12s
check_docs_only	18s
Check formatting and spelling	30s
(Linux) Run Clippy and tests	16m 49s
(Windows) Run Clippy and tests	9m 5s
(macOS) Run Clippy and tests	6m 16s
(Linux) Build Remote Server	2m 18s
Create a macOS bundle	0s
Create arm64 Linux bundle	0s
Create a Linux bundle	0s
Auto release preview	0s
	35m 28s

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