Add first-class transaction support for DBMS in Spin SDKs

It would be really handy to have first-class support for transactions when interacting with DBMS like PostgreSQL or MySQL.

As of today it is possible to concat multiple commands and surround those with BEGIN and COMMIT to use transactions. Although this works, it comes at the cost of ending up with longer TSQL statements.

In contrast, having first-class support for transactions, would result in

• cleaner representation in code
• prevent myself from writing even more plain TSQL
• have compile-time check

See the following (pseudo-code) for illustration.

// ...
let connection = Connection::open(connection_string)?;
let tx = connection::begin_transaction();

let res1 = tx.execute("MY 1ST COMMAND", &params);
let res2 = tx.execute("MY 2ND COMMAND", &params);

match tx.commit() {
  Ok(res) => ,   // ...
  Err(e) => tx.rollback(),      // ...
}

The issue names no repository files or tests. Start by locating the SDK connection flow represented by Connection::open and the proposed begin_transaction, execute, commit, and rollback calls, then compare current PostgreSQL and MySQL command handling. Done means a defined first-class transaction API with compile-time checking and documented commit or rollback behavior.