[aws-docdb] autoMinorVersionUpgrade is not set to true by default

[ryyakobe]

DocDB documentation states that autoMinorVersionUpgrade is set to true by default but it's not.

   /**
   * Indicates that minor engine upgrades are applied automatically to the
   * DB instance during the maintenance window.
   *
   * @default true
   */
  readonly autoMinorVersionUpgrade?: boolean;

It's later used in constructor:

      autoMinorVersionUpgrade: props.autoMinorVersionUpgrade,

so if props.autoMinorVersionUpgrade was not set, then the resulting template will not include AutoMinorVersionUpgrade value at all for AWS::DocDB::DBInstance, but should have AutoMinorVersionUpgrade: true.

Reproduction Steps

This test will fail, because AutoMinorVersionUpgrade is not present.

    // GIVEN
    const stack = testStack();

    // WHEN
    new DatabaseInstance(stack, 'Instance', {
      cluster: stack.cluster,
      instanceClass: SINGLE_INSTANCE_TYPE,
    });

    // THEN
    expectCDK(stack).to(haveResource('AWS::DocDB::DBInstance', {
      Properties: {
        AutoMinorVersionUpgrade: true,
        DBClusterIdentifier: { Ref: 'DatabaseB269D8BB' },
        DBInstanceClass: EXPECTED_SYNTH_INSTANCE_TYPE,
      },
      DeletionPolicy: 'Retain',
      UpdateReplacePolicy: 'Retain',
    }, ResourcePart.CompleteDefinition));

What did you expect to happen?

The above test to pass.

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