refactor(cmd): standardize subcommand aliases with kubectl shortnames

What this PR does / why we need it?

This PR refactors subcommand aliases to match kubectl official shortnames, as disaplyed in kubectl api-resources. Fixes:

Remove excess singular aliases (i.e. "job", "replicaset")
Remove unofficial shortnames (i.e. "scrt")
Support uncovered shortnames (i.e. "crds")

In addition, this PR refactors the Usage section in README.md to address kor's subcommands in singular form.

PR Checklist

[x] This PR adds new code
[x] This PR adds docs

GitHub Issue

[XX-XX]

Notes for your reviewers

Kor Original Aliases

```console $ grep -r Aliases cmd/kor/ -B 1 cmd/kor/clusterroles.go- Use: "clusterrole", cmd/kor/clusterroles.go: Aliases: []string{"clusterroles"}, -- cmd/kor/configmaps.go- Use: "configmap", cmd/kor/configmaps.go: Aliases: []string{"cm", "configmaps"}, -- cmd/kor/crds.go- Use: "customresourcedefinition", cmd/kor/crds.go: Aliases: []string{"crd", "customresourcedefinitions"}, -- cmd/kor/daemonsets.go- Use: "daemonset", cmd/kor/daemonsets.go: Aliases: []string{"ds", "daemonsets"}, -- cmd/kor/deployments.go- Use: "deployment", cmd/kor/deployments.go: Aliases: []string{"deploy", "deployments"}, -- cmd/kor/finalizers.go- Use: "finalizer", cmd/kor/finalizers.go: Aliases: []string{"fin", "finalizers"}, -- cmd/kor/hpas.go- Use: "horizontalpodautoscaler", cmd/kor/hpas.go: Aliases: []string{"hpa", "horizontalpodautoscalers"}, -- cmd/kor/ingresses.go- Use: "ingress", cmd/kor/ingresses.go: Aliases: []string{"ing", "ingresses"}, -- cmd/kor/jobs.go- Use: "job", cmd/kor/jobs.go: Aliases: []string{"job", "jobs"}, -- cmd/kor/pdbs.go- Use: "poddisruptionbudget", cmd/kor/pdbs.go: Aliases: []string{"pdb", "poddisruptionbudgets"}, -- cmd/kor/pods.go- Use: "pod", cmd/kor/pods.go: Aliases: []string{"po", "pods"}, -- cmd/kor/pv.go- Use: "persistentvolume", cmd/kor/pv.go: Aliases: []string{"pv", "persistentvolumes"}, -- cmd/kor/pvc.go- Use: "persistentvolumeclaim", cmd/kor/pvc.go: Aliases: []string{"pvc", "persistentvolumeclaims"}, -- cmd/kor/replicasets.go- Use: "replicaset", cmd/kor/replicasets.go: Aliases: []string{"rs", "replicaset", "replicasets"}, -- cmd/kor/roles.go- Use: "role", cmd/kor/roles.go: Aliases: []string{"roles"}, -- cmd/kor/secrets.go- Use: "secret", cmd/kor/secrets.go: Aliases: []string{"scrt", "secrets"}, -- cmd/kor/serviceaccounts.go- Use: "serviceaccount", cmd/kor/serviceaccounts.go: Aliases: []string{"sa", "serviceaccounts"}, -- cmd/kor/services.go- Use: "service", cmd/kor/services.go: Aliases: []string{"svc", "services"}, -- cmd/kor/statefulsets.go- Use: "statefulset", cmd/kor/statefulsets.go: Aliases: []string{"sts", "statefulsets"}, -- cmd/kor/storageclasses.go- Use: "storageclass", cmd/kor/storageclasses.go: Aliases: []string{"sc", "storageclassses"}, ```

Kubectl Official Shortnames

```console $ kubectl api-resources | awk '{print $1, $2}' | egrep -v '/|v1' | column -t NAME SHORTNAMES componentstatuses cs configmaps cm endpoints ep events ev limitranges limits namespaces ns nodes no persistentvolumeclaims pvc persistentvolumes pv pods po replicationcontrollers rc resourcequotas quota serviceaccounts sa services svc customresourcedefinitions crd,crds daemonsets ds deployments deploy replicasets rs statefulsets sts horizontalpodautoscalers hpa cronjobs cj certificatesigningrequests csr events ev ingresses ing networkpolicies netpol poddisruptionbudgets pdb priorityclasses pc storageclasses sc ```

Files	Patch %	Lines
pkg/kor/multi.go	0.00%	2 Missing :warning:
pkg/kor/all.go	0.00%	1 Missing :warning:

yonahd / kor