Implement changes arising from the 21/22 financial year

This is a scheduled issue to implement changes arising from the 21/22 financial year.

Please note, whoever picks this issue up should remove the other assignees and then raise the following issues a copy of this issue for 22/23 with a due date set to 2022-03-01 (also assign to members of the team so that they are notified when due).

For good measure, an event matching this issue has been added to the shared Google Calendar. This event repeats so no additional action is necessary.

Technical Notes

The actual job requires that you look up the 'Employer (secondary) contribution rates' & 'Class 1 National Insurance thresholds' in the Rates and thresholds for employers 2021 to 2022 and update TABLE_A_EMPLOYER_NIC accordingly.

Please remember to add a version tag to your commit and then raise MRs on the webapp & salaries-commitments projects to deploy the resulting changes.