nm-online: add page; nmtui-{connect,edit,hostname}: add alias pages (#10426)

* nmtui-{connect,edit,hostname}: add alias pages

* nm-online: add page

pages/linux/nm-online.md

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+# nm-online
+
+> Ask NetworkManager whether the network is connected.
+> More information: <https://networkmanager.dev/docs/api/latest/nm-online.html>.
+
+- Find out whether the network is connected and print the result to `stdout`:
+
+`nm-online`
+
+- Wait `n` seconds for a connection (30 by default):
+
+`nm-online --timeout {{n}}`

pages/linux/nmtui-connect.md

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+# nmtui-connect
+
+> This command is an alias of `nmtui connect`.
+
+- View documentation for the original command:
+
+`tldr nmtui`

pages/linux/nmtui-edit.md

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+# nmtui-edit
+
+> This command is an alias of `nmtui edit`.
+
+- View documentation for the original command:
+
+`tldr nmtui`

pages/linux/nmtui-hostname.md

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+# nmtui-hostname
+
+> This command is an alias of `nmtui hostname`.
+
+- View documentation for the original command:
+
+`tldr nmtui`