Add people polkadot genesis chainspec (#5124)

Published as part of the fellowship
[v1.2.6](https://github.com/polkadot-fellows/runtimes/releases/tag/v1.2.6)
release and originally intentionally left out of the repo as the
hardcoded system chains will soon be removed from the
`polkadot-parachain`.

After a conversation in
https://github.com/paritytech/polkadot-sdk/issues/5112 it was pointed
out by @josepot that there should be a single authoritative source for
these chainspecs. Since this is already the place for these it will
serve until something more fitting can be worked out.

cumulus/polkadot-parachain/chain-specs/people-polkadot.json

+../../parachains/chain-specs/people-polkadot.json
\ No newline at end of file

cumulus/polkadot-parachain/src/chain_spec/people.rs

@@ -63,8 +63,9 @@ impl PeopleRuntimeType {
 			PeopleRuntimeType::Kusama => Ok(Box::new(GenericChainSpec::from_json_bytes(
 				&include_bytes!("../../chain-specs/people-kusama.json")[..],
 			)?)),
-			PeopleRuntimeType::Polkadot =>
-				todo!("Generate chain-spec: ../../chain-specs/people-polkadot.json"),
+			PeopleRuntimeType::Polkadot => Ok(Box::new(GenericChainSpec::from_json_bytes(
+				&include_bytes!("../../chain-specs/people-polkadot.json")[..],
+			)?)),
 			PeopleRuntimeType::Rococo => Ok(Box::new(GenericChainSpec::from_json_bytes(
 				&include_bytes!("../../chain-specs/people-rococo.json")[..],
 			)?)),

prdoc/pr_5124.prdoc

+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Add Polkadot Chain genesis chainspec
+
+doc:
+  - audience: Node Operator
+    description: |
+      The Polkadot People Chain can now be run as all other system parachains without specifying a
+      chainspec. However this will soon be deprecated and `--chain ./chainspec.json` should continue
+      to be used instead.
+
+  - audience: Runtime User
+    description: |
+      The Polkadot People Chain chainspecs have been added to the polkadot-sdk repo and can now be
+      pulled from there along with all other system chains.
+
+crates:
+  - name: polkadot-parachain-bin
+    bump: minor