Capture telemetry data on per-user monthly LLM spending (#16050)

Release Notes:

- N/A

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Co-authored-by: Marshall <marshall@zed.dev>

crates/collab/migrations_llm/20240809160000_add_pricing_columns_to_models.sql

@@ -0,0 +1,3 @@
+ALTER TABLE models
+    ADD COLUMN price_per_million_input_tokens integer NOT NULL DEFAULT 0,
+    ADD COLUMN price_per_million_output_tokens integer NOT NULL DEFAULT 0;