Add setting to specify next increment Id increase from 1 to specific number?

Nobody has claimed this yet.

I would like to control the next increment Id generated by data migration tool. The current setup works well, but I have a project that requires a gap between M1 and M2 increment Ids, as the original M1 will continue to process some orders.

### Preconditions
1. Magento 1.14.4.0
2. Magento 2.3.0
3. PHP 7.2.16
4. MySQL 5.7.25

### Steps to reproduce
1. Convert data from Magento 1 to Magento 2
2. Next increment Id is last increment on Magento PLUS 1

e.g. in M1: 308774316
in M2: 308774317

### Expected result
1. Add setting to allow next increment to be: last increment + config setting in settings.xml (e.g. 1, or any number of choosing).

e.g. in M1: 308774316
in M2: 308874316 (using setting of 100000)

### Actual result
1. 308774317

### Additional notes

Start with settings.xml and trace the data migration logic that calculates the next increment ID from the Magento 1 value. Define how a configurable offset should be represented and verify the migrated Magento 2 value against the requested offset. No specific implementation file or test is identified in the issue.

Written by the indexing model from the issue text.