Another sub-problem.

It seems when modifying the value via `juju controller-config` the value `agent-logfile-max-size` is stored as a string in the db which is causing problem.

Reproducer:
1. Bootstrap a controller and enable HA
2. juju controller-config agent-logfile-max-backups=3 # default is 2
3. Reboot one of the controllers and it won't come back (the controller machine is ok)

The machine agent tries start and repeatedly crashes as it can't parse `agent-logfile-max-size`:
```
goroutine 492 [running]:
github.com/juju/juju/controller.Config.mustInt(0x5719d60?, {0x58e56c9, 0x19})
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/controller/config.go:568 +0xf8
github.com/juju/juju/controller.Config.intOrDefault(...)
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/controller/config.go:575
github.com/juju/juju/controller.Config.AgentLogfileMaxBackups(...)
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/controller/config.go:867
github.com/juju/juju/apiserver.newServer({{0x623d8c8, 0x9191b20}, {0x0, 0x0}, {0x6233900, 0xc0007fd030}, {0xc0002ac0c0, 0xd}, {0xc0002ac150, 0xd}, ...})
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/apiserver/apiserver.go:412 +0xc32
github.com/juju/juju/apiserver.NewServer({{0x623d8c8, 0x9191b20}, {0x0, 0x0}, {0x6233900, 0xc0007fd030}, {0xc0002ac0c0, 0xd}, {0xc0002ac150, 0xd}, ...})
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/apiserver/apiserver.go:289 +0xf8
github.com/juju/juju/worker/apiserver.newServerShim({{0x623d8c8, 0x9191b20}, {0x0, 0x0}, {0x6233900, 0xc0007fd030}, {0xc0002ac0c0, 0xd}, {0xc0002ac150, 0xd}, ...})
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/worker/apiserver/worker.go:183 +0x58
github.com/juju/juju/worker/apiserver.NewWorker({{0x6273e50, 0xc000ac24e0}, {0x623d8c8, 0x9191b20}, 0xc0007e2600, {0x6250a60, 0xc0000d8800}, 0xc0004a9b00, {0x6215f08, 0xc0007f3e60}, ...})
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/worker/apiserver/worker.go:179 +0x4d9
github.com/juju/juju/worker/apiserver.ManifoldConfig.start({{0x587ba94, 0x5}, {0x58a6d86, 0x10}, {0x587bc7e, 0x5}, {0x588ef51, 0xb}, {0x5893781, 0xc}, ...}, ...)
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/worker/apiserver/manifold.go:243 +0x843
github.com/juju/juju/cmd/jujud/agent/engine.flagStart.func1({0x6216b38, 0xc000c3c480})
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/cmd/jujud/agent/engine/housing.go:108 +0xb6
github.com/juju/worker/v3/dependency.(*Engine).runWorker.func1()
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/vendor/github.com/juju/worker/v3/dependency/engine.go:518 +0x399
github.com/juju/worker/v3/dependency.(*Engine).runWorker.func2()
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/vendor/github.com/juju/worker/v3/dependency/engine.go:522 +0x53
github.com/juju/worker/v3/dependency.(*Engine).runWorker(0xc00036e480, {0x5889d2e, 0xa}, 0x18da6d0?, 0xc000af2300?, 0xc000c3c480)
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/vendor/github.com/juju/worker/v3/dependency/engine.go:553 +0xeb
created by github.com/juju/worker/v3/dependency.(*Engine).requestStart
        /home/jenkins/workspace/build-juju/build/src/github.com/juju/juju/vendor/github.com/juju/worker/v3/dependency/engine.go:428 +0x6ea
2022-11-19 15:19:47 INFO juju.cmd supercommand.go:56 running jujud [2.9.35 da3416008ea4ce7851a4c967ae191a0044917024 gc go1.19.2]
2022-11-19 15:19:47 DEBUG juju.cmd supercommand.go:57   args: []string{"/var/lib/juju/tools/machine-0/jujud", "machine", "--data-dir", "/var/lib/juju", "--machine-id", "0", "--debug"}
```