Implement redis config dump

[Crunsher]

This example is done for Hosts, but works the same for any other config object

1. Run SCAN on icinga:config:Host:*
2. Check for each results if it still exists
3. Delete those who don't
4. Serialize all fields of objects and write them into redis following Figure out whether we want to store objects "the Redis way" #5118

Possibly we want our checksums there too (refs #5657)