Improve dagger input UX (solve #874)

Add new argument `--show-optional` to `dagger input list`.
Now by default, `dagger input list` will only show required input.
To get all inputs (including those with default value), you can use
that new argument.

Test has been updated to support changes.

Signed-off-by: Tom Chauveau <tom.chauveau@epitech.eu>

tests/core.bats

@@ -20,7 +20,7 @@ setup() {
     dagger_new_with_plan test-core "$TESTDIR"/core/inputs-outputs
 
     # List available inputs
-    run dagger -e test-core input list
+    run dagger -e test-core input list --show-optional
     assert_success
     assert_output --partial 'name'
     assert_output --partial 'dir'