Convert PortForwarder to Accessor, move to Deployer

[nkubala]

Related: #5813, #5936

Description
This change creates a new object, Accessor, which is responsible for accessing deployed resources from Skaffold. This object is a conversion of the original PortForward object, and is a superset of it. The Accessor is moved from the Runner to the Deployer, since accessor-behavior is implicitly tied to the underlying Deployer implementation. See #5809 for a more detailed description of why we need to do this.

This change adds one method to the Deployer interface:

type Deployer interface {
  ...

  GetAccessor() access.Accessor
}

The GetAccessor() method is used by the Runner to retrieve the Accessor implementation and actually orchestrate that behavior in the dev loop.

[codecov]

Codecov Report

Merging #6026 (9104599) into master (e01d089) will decrease coverage by 0.00%.
The diff coverage is 65.78%.

@@            Coverage Diff             @@
##           master    #6026      +/-   ##
==========================================
- Coverage   70.75%   70.75%   -0.01%     
==========================================
  Files         464      466       +2     
  Lines       17928    17956      +28     
==========================================
+ Hits        12685    12704      +19     
- Misses       4313     4321       +8     
- Partials      930      931       +1     

Impacted Files	Coverage Δ
pkg/skaffold/access/access_mux.go	0.00% <0.00%> (ø)
pkg/skaffold/deploy/deploy_mux.go	65.90% <0.00%> (-4.83%)	⬇️
pkg/skaffold/deploy/label/labeller.go	68.75% <ø> (ø)
...affold/kubernetes/portforward/kubectl_forwarder.go	69.50% <ø> (-0.22%)	⬇️
...kubernetes/portforward/port_forward_integration.go	0.00% <0.00%> (ø)
pkg/skaffold/access/provider.go	50.00% <50.00%> (ø)
pkg/skaffold/deploy/helm/deploy.go	78.68% <50.00%> (-0.24%)	⬇️
pkg/skaffold/deploy/kpt/kpt.go	81.33% <50.00%> (-0.22%)	⬇️
pkg/skaffold/deploy/kubectl/kubectl.go	68.68% <50.00%> (-0.20%)	⬇️
pkg/skaffold/deploy/kustomize/kustomize.go	75.00% <50.00%> (-0.35%)	⬇️
... and 16 more

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[tejal29]

This is a little bit confusing. Are all providers supposed to provide a no-op and kubernetes accessor?

Do we need a provider here?

[nkubala]

all providers should contain an implementation for each "style" of deployer we support in skaffold - right now there are only Kubernetes deployers (and they all share the same underlying logging/debugging/accessing implementations), but in the future we'll have alternate implementations.

I like this approach because it makes it clear what the different implementations for each component are, and also makes it clear where they can be obtained from (since they rely on dependencies that are injected via closures on the constructors). definitely open to suggestions for alternative approaches here though.