Document running custom JDBC operations

[jatcwang]

Since #2064 we have better ways for users to customize their JDBC execution more while still retaining the ability to log and measure execution times.

We should document how to:

• Extract the individual "steps" from a fragment (Need Query / Update: Allow extracting the individual steps (create PS, set params, etc) #2065)
• Plug the various "steps" into doobie.hi.executeWithResultSet/executeWithoutResultSet while customizing some of the steps (e.g. running executeLargeUpdate instead of executeUpdate)