Gather benchmarks data for the following parts of pgroll:

• Backfill duration - How long does it take to perform backfill operations on a table of some fixed size (say 10^7 rows)?
• Effect of dual writes - What overhead do the up/down triggers incur on UPDATE heavy tables?
• read_schema query performance - Benchmark the performance of the read_schema query, run on every DDL statement to capture 'inferred' migrations.
• Persist results somewhere so we can see changes over time

Having these benchmarks in place would allow us to measure performance improvements over time and avoid regressions.