Feature request: Add activeMonth and activeHalfyear into usage.users in the nodeinfo.

The number of monthly active users is already in the /api/v1/instance by !3283 (merged), but the API is not suit for standards. In the nodeinfo standard, activeMonth and activeHalfyear should be at the usage.users section.

This feature will have a practical application: https://the-federation.info/ 's lists of instances are sorted by the active monthly users. Now the sort does not work well for the Pleroma instances, however, this feature will fix it.