chore: Extract PromptStore out of prompt_library (#25837)

One step closer to removing long pole with assistant/assistant2 builds

Release Notes:

- N/A

crates/collab/Cargo.toml

@@ -111,7 +111,7 @@ node_runtime.workspace = true
 notifications = { workspace = true, features = ["test-support"] }
 pretty_assertions.workspace = true
 project = { workspace = true, features = ["test-support"] }
-prompt_library.workspace = true
+prompt_store.workspace = true
 recent_projects = { workspace = true }
 release_channel.workspace = true
 remote = { workspace = true, features = ["test-support"] }