feat: add IFU functionality

[civsiv]

This PR adds IndividualFacilityUse functionality to Server.NET.

In order to fully finish off this PR the following needs to happen (apart from the review comments below):

1. an appsettings.ifu.json file needs to be added to this PR (or based on the comment below re default FU vs IFU behaviour, an appsettings.fuNoIfu.json)
2. In Test Suite, an env file needs to be added to run Test Suite in IFU mode
3. This branch needs to be renamed to be coverage/ifus so that the Test Suite branch in 2 run tests against this branch
4. Add individual facility uses to the Github Actions test matrix so that every CI run also runs IFU tests

[nickevansuk]

In addition to suggested changes previously discussed

[lukehesluke]

As mentioned here: #201 (comment), this IFU PR includes the changes from #201. So, if this IFUs PR gets merged first, please could the merger then close #201? Thanks

[nickevansuk]

As per this PR's description, a new PR has been created #204 in order to rename the branch to coverage/ifus