Set tenancy by creating new PrometheusRule obj for Thanos Operator

[saswatamcode]

This changes the PrometheusRule syncer path to do the following,

• Removes obsctl operations (setting tenant context, and then setting rules), after collecting PrometheusRule objects and splitting tenants
• Replaces this with a function that creates a new PrometheusRule object for each tenant with rule groups pertaining to that tenant. It also uses prom-label-proxy to inject tenant labels into the rules of the tenant
• Also ensures that new PrometheusRule objects have Thanos Operator labels

This PR also updates Go version, lint tooling and a bunch of k8s, Prometheus Operator specific dependencies

[philipgough]

/lgtm