cmdkey: add page (#10430)

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/windows/cmdkey.md

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+# cmdkey
+
+> Create, show, and delete stored user names and passwords.
+> More information: <https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/cmdkey>.
+
+- Show a list of all user credentials:
+
+`cmdkey /list`
+
+- Store credentials for a user that accesses a server:
+
+`cmdkey /add:{{server_name}} /user:{{user_name}}`
+
+- Delete credentials for a specific target:
+
+`cmdkey.exe /delete {{target_name}}`