Runtime: allow backing multiple candidates of same parachain on different cores (#3231)

Fixes https://github.com/paritytech/polkadot-sdk/issues/3144

Builds on top of https://github.com/paritytech/polkadot-sdk/pull/3229

### Summary
Some preparations for Runtime to support elastic scaling, guarded by
config node features bit `FeatureIndex::ElasticScalingMVP`. This PR
introduces a per-candidate `CoreIndex` but does it in a hacky way to
avoid changing `CandidateCommitments`, `CandidateReceipts` primitives
and networking protocols.

#### Including `CoreIndex` in `BackedCandidate`
If the `ElasticScalingMVP` feature bit is enabled then
`BackedCandidate::validator_indices` is extended by 8 bits.
The value stored in these bits represents the assumed core index for the
candidate.

It is temporary solution which works by creating a mapping from
`BackedCandidate` to `CoreIndex` by assuming the `CoreIndex` can be
discovered by checking in which validator group the validator that
signed the statement is.

TODO:
- [x] fix tests
- [x] add new tests
- [x] Bump runtime API for Kusama, so we have that node features thing!
-> https://github.com/polkadot-fellows/runtimes/pull/194

---------

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>
Signed-off-by: alindima <alin@parity.io>
Co-authored-by: alindima <alin@parity.io>

polkadot/zombienet_tests/functional/0012-enable-node-feature.js

@@ -0,0 +1,37 @@
+async function run(nodeName, networkInfo, index) {
+  const { wsUri, userDefinedTypes } = networkInfo.nodesByName[nodeName];
+  const api = await zombie.connect(wsUri, userDefinedTypes);
+
+  await zombie.util.cryptoWaitReady();
+
+  // account to submit tx
+  const keyring = new zombie.Keyring({ type: "sr25519" });
+  const alice = keyring.addFromUri("//Alice");
+
+  await new Promise(async (resolve, reject) => {
+    const unsub = await api.tx.sudo
+      .sudo(api.tx.configuration.setNodeFeature(Number(index), true))
+      .signAndSend(alice, ({ status, isError }) => {
+        if (status.isInBlock) {
+          console.log(
+            `Transaction included at blockhash ${status.asInBlock}`,
+          );
+        } else if (status.isFinalized) {
+          console.log(
+            `Transaction finalized at blockHash ${status.asFinalized}`,
+          );
+          unsub();
+          return resolve();
+        } else if (isError) {
+          console.log(`Transaction error`);
+          reject(`Transaction error`);
+        }
+      });
+  });
+
+
+
+  return 0;
+}
+
+module.exports = { run };