kubectl-cp: add page

[girdharagrawalbro]

Adds documentation for the kubectl cp subcommand that copies files to/from containers.

Closes part of #17606 (kubectl troubleshooting and debugging commands).

Changes

• Created pages/common/kubectl-cp.md with 5 practical examples
• Covers bidirectional copy operations for files and directories
• Includes namespace and multi-container pod examples
• Follows style guide: imperative mood, clear path syntax, proper placeholders

Examples

• Copy local file to pod
• Copy file from pod to local
• Copy directory recursively
• Copy with namespace specification
• Use specific container in multi-container pod

[CLAassistant]

All committers have signed the CLA.

[Managor]

Apply to whole page

[Managor]

Suggested change

	`kubectl cp {{path/to/local_file}} {{pod_name}}:{{/path/in/pod}}`
	`kubectl cp {{path/to/local_file}} {{pod_name}}:/{{path/in/pod}}`

Leave the initial slash outside the placeholder to indicate that it's mandatory and always an absolute path

[Managor]

Apply the suggestion to all examples