Configure Alloy to be used as a self-service too for logs (source files)

[TheoBrigitte]

Towards: giantswarm/roadmap#3518

[TheoBrigitte]

Change this to use a giantswarm image

[TheoBrigitte]

Still needs to implement the tenant name override from label, like its done here https://github.com/giantswarm/logging-operator/pull/233/files#diff-405f451506c2146b4cf915863a848d9a42f39a3b292a9b6f9ada78b4eac32598R85

[TheoBrigitte]

Not following this route as it would not allow to override the tenant when using labels on namespaces, due to the namespaces labels not being available when using discovery.kubernetes.

Trying to discover those labels using a sidecar container also does not work, the idea was to fetch the namespace label and produce a list of namespace_A:tenant_name_A;namespace_B:tenant_name_B; and then extract the tenant name using the following relabel rule

rule {
        source_labels = concat(["__meta_kubernetes_namespace"], split(local.file.namespaces_tenant.content, ";"))
       regex         = "(.+);.*(\1):([0-9]+);.*"

        target_label  = "tenant_namespace"
}

Unfortunately there is no support for backreference (\1) in Alloy/Prometheus regex RE2 engine.

Also this would be super hacky and any other namespace label we would like to process would introduce another hack.