Ability to persist hashed source data to reconcilation DB

[chadlwilson]

Context / Goal

A core feature of the design is to be able to take data from a source DB, load the rows and hash the data and then persist them to a reconciliation DB in hashed form, that can be later compared to target.

We can start by being able to stream data

Expected Outcome

• Be able to execute an arbitrary dataset query, expressed as SQL, against a configured source DB
• Hash the column values other than a designated MigrationKey using SHA256
  • start off with handling for columns that can be mapped easily to core Java types (boolean, integer numerics, floating points, strings)
• Be able to persist the (migrationKey, sourceHashValue) to a 3rd "reconciliation DB" owned by the reconciliation tool

Out of Scope

• Loading data from the target DB (Ability to persist/merge hashed target data into reconcilation DB #18)
• Producing a report of the results (Persist reconcilation report results in a queryable manner #12)
• performance testing (Exploratory performance testing of load and persist #26)

Additional context / implementation notes

• Assume using an initial approach based on Spike use of r2dbc to stream data off databases #20