Support CustomRun list command.

[stillfox-lee]

Ref: #1623 (comment)

I plan to implement the List command for CustomRun. Since the label of CustomTask is custom, the main difference between it and TaskRun is that it does not support filtering by the "Name".

UI Example

tkn customruns -h
Manage CustomRuns

Usage:
tkn customrun [flags]
tkn customrun [command]

Aliases:
customrun, cr, customruns

Available Commands:
list Lists CustomRuns in a namespace

Flags:
-c, --context string name of the kubeconfig context to use (default: kubectl config current-context)
-h, --help help for customrun
-k, --kubeconfig string kubectl config file (default: $HOME/.kube/config)
-n, --namespace string namespace to use (default: from $KUBECONFIG)
-C, --no-color disable coloring (default: false)

---

tkn customruns list -h
Lists CustomRuns in a namespace

Usage:
tkn customrun list [flags]

Aliases:
list, ls

Examples:
List all CustomRuns in namespace 'bar':

tkn cr list -n bar

Flags:
-A, --all-namespaces list CustomRuns from all namespaces
--allow-missing-template-keys If true, ignore any errors in templates when a field or map key is missing in the template. Only applies to golang and jsonpath output formats. (default true)
-h, --help help for list
--label string A selector (label query) to filter on, supports '=', '==', and '!='
--limit int Limits the number of CustomRuns. If the limit value is 0 returns all
--no-headers do not print column headers with output (default print column headers with output)
-o, --output string Output format. One of: (json, yaml, name, go-template, go-template-file, template, templatefile, jsonpath, jsonpath-as-json, jsonpath-file).
--reverse list CustomRuns in reverse order
--show-managed-fields If true, keep the managedFields when printing objects in JSON or YAML format.
--template string Template string or path to template file to use when -o=go-template, -o=go-template-file. The template format is golang templates [http://golang.org/pkg/text/template/#pkg-overview].

Global Flags:
-c, --context string name of the kubeconfig context to use (default: kubectl config current-context)
-k, --kubeconfig string kubectl config file (default: $HOME/.kube/config)
-n, --namespace string namespace to use (default: from $KUBECONFIG)
-C, --no-color disable coloring (default: false)

[vdemeester]

/kind feature

[piyush-garg]

assign @stillfox-lee

[piyush-garg]

/assign @stillfox-lee