Rococo & Westend People Chain (#2281)

Rococo and Westend runtimes for the "People Chain". This chain contains
the Identity pallet with plans to migrate all related data from the
Relay Chain.

Changes `IdentityInfo` to:

- Remove `additional_fields`.
- Add `github` and `discord` as first class fields. From scraping chain
data, these were the only two additional fields used (for the Fellowship
and Ambassador Program, respectively).
- Rename `riot` to `matrix`.

Note: This will use the script in
https://github.com/paritytech/polkadot-sdk/pull/2025 to generate the
genesis state.

TODO:

- [x] https://github.com/paritytech/polkadot-sdk/pull/1814 and
integration of the Identity Migrator pallet for migration.
- [x] Tests: https://github.com/paritytech/polkadot-sdk/pull/2373

---------

Co-authored-by: Muharem <ismailov.m.h@gmail.com>
Co-authored-by: Michal Kucharczyk <1728078+michalkucharczyk@users.noreply.github.com>
Co-authored-by: Dónal Murray <donal.murray@parity.io>
Co-authored-by: Richard Melkonian <35300528+0xmovses@users.noreply.github.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

cumulus/parachains/integration-tests/emulated/networks/westend-system/Cargo.toml

@@ -18,3 +18,4 @@ asset-hub-westend-emulated-chain = { path = "../../chains/parachains/assets/asse
 bridge-hub-westend-emulated-chain = { path = "../../chains/parachains/bridges/bridge-hub-westend" }
 collectives-westend-emulated-chain = { path = "../../chains/parachains/collectives/collectives-westend" }
 penpal-emulated-chain = { path = "../../chains/parachains/testing/penpal" }
+people-westend-emulated-chain = { path = "../../chains/parachains/people/people-westend" }