executeRead (work, transactionConfig) {
    return this._executeInTransaction(ACCESS_MODE_READ, work, transactionConfig)
  }
Executes the provided unit of work in a {@link READ} reactive transaction which is created with the provided
transaction configuration.
@public
@param {function(txc: RxManagedTransaction): Observable} work - A unit of work to be executed.
@param {TransactionConfig} transactionConfig - Configuration for the enclosing transaction created by the driver.
@returns {Observable} - A reactive stream returned by the unit of work.