## What
This change moves the `linkerd check --multicluster` functionality under it's
own multicluster subcommand: `linkerd multicluster check`.
There should be no functional changes as a result of this change. `linkerd
check` no longer checks for anything multicluster related and the
`--multicluster` flag has been removed.
## Why
Closes#5208
The bulk of these changes are moving all the multicluster checks from
`pkg/healthcheck` into the multicluster package.
Doing this completely separates it from core Linkerd. It still uses
`pkg/healtcheck` when possible, but anything that is used only by `multicluster
check` has been moved.
**Note the the `kubernetes-api` and `linkerd-existence` checks are run.**
These checks are required for setting up the Linkerd health checker. They set
the health checker's `kubeAPI`, `linkerdConfig`, and `apiClient` fields.
These could be set manually so that the only check the user sees is
`linkerd-multicluster`, but I chose not to do this.
If any of the setting functions errors, it would just tell the user to run
`linkerd check` and ensure the installation is correct. I find the user error
handling to be better by including these required checks since they should be
run in the first place.
## How to test
Installing Linkerd and multicluster should result in a basic check output:
```
$ bin/linkerd install |kubectl apply -f -
..
$ bin/linkerd check
..
$ bin/linkerd multicluster install |kubectl apply -f -
..
$ bin/linkerd multicluster check
kubernetes-api
--------------
√ can initialize the client
√ can query the Kubernetes API
linkerd-existence
-----------------
√ 'linkerd-config' config map exists
√ heartbeat ServiceAccount exist
√ control plane replica sets are ready
√ no unschedulable pods
√ controller pod is running
√ can initialize the client
√ can query the control plane API
linkerd-multicluster
--------------------
√ Link CRD exists
Status check results are √
```
After linking a cluster:
```
$ bin/linkerd multicluster check
kubernetes-api
--------------
√ can initialize the client
√ can query the Kubernetes API
linkerd-existence
-----------------
√ 'linkerd-config' config map exists
√ heartbeat ServiceAccount exist
√ control plane replica sets are ready
√ no unschedulable pods
√ controller pod is running
√ can initialize the client
√ can query the control plane API
linkerd-multicluster
--------------------
√ Link CRD exists
√ Link resources are valid
* k3d-y
√ remote cluster access credentials are valid
* k3d-y
√ clusters share trust anchors
* k3d-y
√ service mirror controller has required permissions
* k3d-y
√ service mirror controllers are running
* k3d-y
× all gateway mirrors are healthy
probe-gateway-k3d-y.linkerd-multicluster mirrored from cluster [k3d-y] has no endpoints
see https://linkerd.io/checks/#l5d-multicluster-gateways-endpoints for hints
Status check results are ×
```
Signed-off-by: Kevin Leimkuhler <kevin@kleimkuhler.com>
Fixes#5257
This branch movies mc charts and cli level code to a new
top level directory. None of the logic is changed.
Also, moves some common types into `/pkg` so that they
are accessible both to the main cli and extensions.
Signed-off-by: Tarun Pothulapati <tarunpothulapati@outlook.com>