Metadata V16 (unstable): Enrich metadata with associated types of config traits (#5274)

This feature is part of the upcoming metadata V16. The associated types
of the `Config` trait that require the `TypeInfo` or `Parameter` bounds
are included in the metadata of the pallet. The metadata is not yet
exposed to the end-user, however the metadata intermediate
representation (IR) contains these types.

Developers can opt out of metadata collection of the associated types by
specifying `without_metadata` optional attribute to the
`#[pallet::config]`.

Furthermore, the `without_metadata` argument can be used in combination
with the newly added `#[pallet::include_metadata]` attribute to
selectively include only certain associated types in the metadata
collection.

### API Design

- There is nothing to collect from the associated types:

```rust
#[pallet::config]
pub trait Config: frame_system::Config {
		// Runtime events already propagated to the metadata.
		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;

		// Constants are already propagated.
		#[pallet::constant]
		type MyGetParam2: Get<u32>;
	}
```

- Default automatic collection of associated types that require TypeInfo
or Parameter bounds:

```rust
	#[pallet::config]
	pub trait Config: frame_system::Config {
		// Runtime events already propagated to the metadata.
		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;

		// Constants are already propagated.
		#[pallet::constant]
		type MyGetParam2: Get<u32>;

		// Associated type included by default, because it requires TypeInfo bound.
		/// Nonce doc.
		type Nonce: TypeInfo;

		// Associated type included by default, because it requires
		// Parameter bound (indirect TypeInfo).
		type AccountData: Parameter;

		// Associated type without metadata bounds, not included.
		type NotIncluded: From<u8>;
	}
```

- Disable automatic collection

```rust
// Associated types are not collected by default.
	#[pallet::config(without_metadata)]
	pub trait Config: frame_system::Config {
		// Runtime events already propagated to the metadata.
		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;

		// Constants are already propagated.
		#[pallet::constant]
		type MyGetParam2: Get<u32>;

		// Explicitly include associated types.
		#[pallet::include_metadata]
		type Nonce: TypeInfo;

		type AccountData: Parameter;

		type NotIncluded: From<u8>;
	}
```

Builds on top of the PoC:
https://github.com/paritytech/polkadot-sdk/pull/4358
Closes: https://github.com/paritytech/polkadot-sdk/issues/4519

cc @paritytech/subxt-team

---------

Signed-off-by: Alexandru Vasile <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Guillaume Thiolliere <[email protected]>
Co-authored-by: Shawn Tabrizi <[email protected]>