Add benchmarks to inform performance-oriented refactoring

[mehcode]

• Establish a new connection.
• Checkout an existing ( and idle ) connection from the pool.
• Ping a connection.
• Small query, small results ( following the specs over at tech empower: https://github.com/TechEmpower/FrameworkBenchmarks/wiki/Project-Information-Framework-Tests-Overview#single-database-query ). Do nothing with the results.
• Small query, huge results ( 10K rows with at least 5 columns where 2 of the columns are String and Vec<u8> ). Do nothing with the results.

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Preferably these can run locally with a single script that uses docker to spin up/down database servers as needed to test all supported databases and versions.

I'm imagining a bench/ or perf/ folder that contains a run.sh script that does the "magic" but I'm pretty open here.

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Update: We now have a docker-compose file that can spin up a database/version pair. This was one of the blockers here.