Improve package structure

[rfranzke]

How to categorize this PR?

/area dev-productivity
/kind enhancement

What this PR does / why we need it:

• Move monitoring-related components to pkg/component/monitoring/*
• Move Gardener components to pkg/component/gardener/*
• Move autoscaling-related components to pkg/component/autoscaling/*
• Move networking-related components to pkg/component/networking/*
• Move Garden cluster-related components to pkg/component/garden/*
• Move Seed cluster-related components to pkg/component/seed/*
• Move Shoot cluster-related components to pkg/component/shoot/*
• Move node mgmt-related components to pkg/component/nodemanagement/*
• Move observability-related components to pkg/component/observability/*
• Move etcd-related components to pkg/component/etcd/*
• Move Kubernetes components to pkg/component/kubernetes/*
• Move pkg/envtest to test/envtest
• Move pkg/mock to third_party/mock
• Move pkg/{openapi,registry} packages to pkg/apiserver/*
• Move pkg/operation to pkg/gardenlet/operation

Release note:

The `pkg/envtest` package has been moved to `test/envtest`. Most component packages in `pkg/component` have been moved. The `pkg/openapi` and `pkg/registry` packages have been moved to `pkg/apiserver/*`.

[acumino]

/assign

[plkokanov]

I managed to go through most of the commits, and plan to try out the PR locally as well.

I just have one question for now - is the nodemanagement/* location ok for the dependency-watchdog? It seems to fit the prober component of the dependency-watchdog, but not the weeder.
As an alternative, I could suggest using the seed/* directory, but don't really have too strong of an opinion.

[plkokanov]

/assign

[rfranzke]

I managed to go through most of the commits, and plan to try out the PR locally as well.

I just have one question for now - is the nodemanagement/* location ok for the dependency-watchdog? It seems to fit the prober component of the dependency-watchdog, but not the weeder. As an alternative, I could suggest using the seed/* directory, but don't really have too strong of an opinion.

I think it shouldn't matter much - I'd prefer to keep it as is since DWD's main task is preventing massive node terminations when getting unavailable.

[acumino]

/lgtm

[gardener-prow]

LGTM label has been added.

Git tree hash: b7f8cf61aef4921158b15fadc502b5593072678d