add .svc suffix to alertmanager address

[bavarianbidi]

To make Silence Operator work behind a corporate proxy, we have to inject the HTTP_PROXY, HTTPS_PROXY and NO_PROXY variable.

To keep the NO_PROXY list as "simple" as possible, following in-cluster-specific values are configured:
<baseDomain>,<podCIDRBlock>,<serviceCIDRBlock>,<external_k8s_API_IP>.

To not change every application to make use of the FQDN (as baseDomain could differ) i've decided to add svc to the NO_PROXY list.

The change of the alertmanager address from alertmanager-operated.monitoring to alertmanager-operated.monitoring.svc should be a no op for all existing clusters.

towards: giantswarm/roadmap#1423
xref: giantswarm/prometheus-meta-operator#1010

Checklist

• Update changelog in CHANGELOG.md.

[QuentinBisson]

I'll try to test it tomorrow

[bavarianbidi]

go 1.19 update + golangci-lint fix: #232

[TheoBrigitte]

LGTM when tested

[bavarianbidi]

LGTM when tested

@TheoBrigitte as i didn't worked with the silence-operator so far: how can i test it? what are the test-cases i have to do?

[TheoBrigitte]

The way to test silence-operator is to basically restart alertmanager check the operator logs and making sure the correct silences where created in alertmanager.