Implement changes arising from the 20/21 financial year

This is a scheduled issue to implement changes arising from the 20/21 financial year.

Please note, whoever picks this issue up should remove the other assignees and then raise the following issues:

• an issue in the webapp to deploy the resulting changes
• an issue in the salaries-commitments to deploy the resulting changes
• a copy of this issue for 21/22 with a due date set to 2021-03-01 (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 2020 to 2021 and update TABLE_A_EMPLOYER_NIC accordingly.