collab: Track cache writes/reads in LLM usage (#18834)

This PR extends the LLM usage tracking to support tracking usage for
cache writes and reads for Anthropic models.

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Antonio <antonio@zed.dev>

crates/collab/migrations_llm/20241007173634_add_cache_token_counts.sql

@@ -0,0 +1,11 @@
+alter table models
+    add column price_per_million_cache_creation_input_tokens integer not null default 0,
+    add column price_per_million_cache_read_input_tokens integer not null default 0;
+
+alter table usages
+    add column cache_creation_input_tokens_this_month bigint not null default 0,
+    add column cache_read_input_tokens_this_month bigint not null default 0;
+
+alter table lifetime_usages
+    add column cache_creation_input_tokens bigint not null default 0,
+    add column cache_read_input_tokens bigint not null default 0;