helm: promote autoscaling to stable

https://github.com/grafana/mimir/pull/7282 added autoscaling to Helm as an experimental feature. This issue is about remaining work in order to promote autoscaling to stable.

The goal of this issue is to promote existing autoscaling support stable. This includes (ruler-)querier, distributor, (ruler-)query-frontend, and ruler. It does not include store-gateways and ingesters.

Bugs

• https://github.com/grafana/mimir/issues/7473

Docs/Migration procedure

• https://github.com/grafana/mimir/issues/7367

Remote URL UX

• Support a remote different from the metamonitoring setup https://github.com/grafana/mimir/pull/7392
• Take the additional headers and auth from metamonitoring setup. Currently basic auth and extra headers are ignored.
• Default to X-Scope-OrgID: metamonitoring if the config is already sending metrics to the same Mimir installation (the same way that metamonitoring computes it)
• Add validation that is same mimir cluster is used, then metamonitoring is also enabled

Helm-jsonnet diffing

• Add helm-jsonnet diffing so that the autoscaling configs don't get out of sync when we change one and forget to change the other. This is a matter of enabling autoscaling on select components in these two files and then making sure there are no differences between the rendered manifests. Minor differences can still be ignored via kustomiztions like this one

Make dashbaords compatible with helm-deployed KEDA objects

• Similar to the /operations/mixin changes in https://github.com/grafana/mimir/pull/4687 - the matchers for keda objects should allow for helm-deployed objects
• https://github.com/grafana/mimir/issues/9431