Add a schema to extensions, to prevent installing extensions on too old of a Zed version (#9599)

Release Notes:

- N/A

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

crates/collab/migrations/20240320124800_add_extension_schema_version.sql

@@ -0,0 +1,2 @@
+-- Add migration script here
+ALTER TABLE extension_versions ADD COLUMN schema_version INTEGER NOT NULL DEFAULT 0;