Generate sql_exporter config files with Jsonnet

There are quite a few benefits to this approach:

- Reduce config duplication
  - The two sql_exporter configs were super similar with just a few
    differences
- Pull SQL queries into standalone files
  - That means we could run a SQL formatter on the file in the future
  - It also means access to syntax highlighting
- In the future, run different queries for different PG versions
  - This is relevant because right now, we have queries that are failing
    on PG 17 due to catalog updates

Signed-off-by: Tristan Partin <tristan@neon.tech>

compute/etc/sql_exporter/pg_stats_userdb.sql

@@ -0,0 +1,10 @@
+-- We export stats for 10 non-system databases. Without this limit it is too
+-- easy to abuse the system by creating lots of databases.
+
+SELECT pg_database_size(datname) AS db_size, deadlocks, tup_inserted AS inserted,
+  tup_updated AS updated, tup_deleted AS deleted, datname
+FROM pg_stat_database
+WHERE datname IN (
+  SELECT datname FROM pg_database
+  WHERE datname <> 'postgres' AND NOT datistemplate ORDER BY oid LIMIT 10
+);