fix: hide internal alias flags from help output

[immanuwell]

small help output papercut.

right now nerdctl --help shows internal alias shim flags like -a, --a, -H, --H, -n, --n. same thing in nerdctl compose --help with -f, --f. looks a bit weird, and not really what users should see.

this hides those shim flags from help, and shows aliases on the real flag line instead. alias parsing still works, so no behavior change there.

repro

go build ./cmd/nerdctl
./nerdctl --help
./nerdctl compose --help

before

-a, --a string
-H, --H string
-n, --n string
-f, --f stringArray

after

--address string ... (aliases: -a, -H, --host)
--namespace string ... (aliases: -n)
--file stringArray ... (aliases: -f)

checks

go test ./cmd/nerdctl -run 'TestRootHelpHidesAliasImplementationFlags|TestRootHiddenAliasesStillParse'
go test ./cmd/nerdctl/compose -run 'TestComposeHelpHidesAliasImplementationFlags|TestComposeHiddenFileAliasStillParses'