WIP: Integrate checks

[christophlehmann]

Adds good old caretaker checks

Checks/Resolvers:

[x] Configuration value
[x] Extension version
[x] Extension state
[x] Core version
[x] HTTP Headers (Pass full client response to resolvers)
[x] Backend users which should be inactive

Others:
[x] Better overview for rules? Currently they just extend the extra fields in client table
[x] Handle failed rules (client is missing needed providers and does not return needed data)
[ ] Labels

For review use https://github.com/christophlehmann/t3monitoring_client/tree/add-check-provider as client