objectify alertmanager config

Update client_golang for wrappable registerer

*: Update to Prometheus v2.4.3

With pinning the kube-prometheus dependency for the generated
`/manifest` folder, one needs to update the `jsonnetfile.lock.json` on
`*.jsonnet` file changes.

this way it will be possible to merge configs

*: Update to Prometheus 2.4.0

contrib/kube-prometheus: Set antiAffinity for Prometheus & Alertmanager

contrib/kube-prometheus: Generate new manifests with antiAffinity

contrib/kube-prometheus: jb update

Documentation: Generate after updating kube-prometheus manifests

contrib/kube-prometheus: Move antiaffinity into own jsonnet file

foobar

This is distributed as a library that the user is meant to import.
example:

```
kp =  (import 'kube-prometheus/kube-prometheus.libsonnet') +
      (import 'kube-prometheus/kube-prometheus-thanos.libsonnet') +
      {
        _config+:: {...}
      };
```

With those changes, diff does show any differences between generated manifests
with and without the version override in a top level jsonnet file.

kube-prometheus: Add Prometheus Operator alerts