Branch add-pallet needs to check for duplicated entries.

[al3mart]

The command pop add pallet in branch add-pallet will inject the different features for the pallet independently of these being already present in the file.

This can be reproduce by running twice the same command, for instance: pop add pallet template -r runtime/src/lib.rs within a parachain project.

It will also instantiate multiple times the same pallet in the runtime.

[evilrobot-01]

The entry API to toml_edit could be useful for this:

pop-cli/src/parachains/zombienet.rs

Lines 148 to 149 in 7dc2e5d

	let Item::Table(settings) =
	network_config.entry("settings").or_insert(Item::Table(Table::new()))

[AlexD10S]

I close the issue for now as we still don't have the pop add pallet functionality